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1
Kretz, Ralph. "Petrology of veined gneisses of the Otter complex, southern Grenville Province." Canadian Journal of Earth Sciences 31, no. 5 (May 1, 1994): 835–51. http://dx.doi.org/10.1139/e94-077.
Повний текст джерелаАнотація:
A prominent metamorphic complex composed mainly of K-feldspar gneiss, with many quartz–feldspar layers and veins, occurs in the Otter Lake terrane of the southern Grenville Province of the Canadian Shield. Intense deformation of the complex is indicated by folded and disjointed amphibolite dikes; many veins are also folded. The K-feldspar gneiss consists of quartz, plagioclase, K-feldspar, biotite, local garnet, and rare sillimanite. With few exceptions, the mineral assemblage of each vein is the same as that of the enclosing gneiss, including garnet and sillimanite, where present, and minor minerals, magnetite, zircon, apatite, and allanite. The volume fraction K-feldspar/(K-feldspar + plagioclase) ranges widely (from 0.05 to 0.90), but compared with adjacent gneiss, K-feldspar is always higher and biotite is lower. The chemical composition of veins is similar to that of enclosing gneiss, but K and Ba are higher and Mg, Fe, Mn, Ti, Zr, Rb, and P are lower. The bulk composition of veined gneiss where veins are numerous and that of adjoining gneiss where veins are scarce are virtually identical. Vein–gneiss differences in plagioclase and garnet composition are small or imperceptible.These results lead to the conclusion that many of the veins were locally derived. The rearrangement of atoms needed to produce a vein is considered in terms of Orville–Fisher exchange reactions, e.g., the transport of K, Al, and Si from gneiss to sites of vein growth, in exchange for Mg, Fe, and H. The Ramberg–Robin model of metamorphic differentiation, in which transport occurs by crystal-boundary diffusion, driven by pressure gradients, is proposed as the principal process of vein formation.
2
Neiva, A. M. R. "Distribution of trace elements in feldspars of granitic aplites and pegmatites from Alijó-Sanfins, northern Portugal." Mineralogical Magazine 59, no. 394 (March 1995): 35–45. http://dx.doi.org/10.1180/minmag.1995.59.394.04.
Повний текст джерелаАнотація:
AbstractAt Alijó-Sanfins there are many granitic aplite and pegmatite veins crosscutting different petrographic facies of the Hercynian granite batholith and also mica-schists. They are tin-bearing granitic rocks. Thirty-four samples of K-feldspar and 34 of albite from these veins and host granites were analysed to establish the distribution of elements and their fractionation trends in the sequence of feldspar crystallization. Rubidium and Cs increase, and Ba, Sr, Ba/K, Sr/K and K/Rb decrease in K-feldspar, whereas Na increases and Sr and Ca decrease in albite, from granites to aplites and pegmatites. In a few aplite-pegmatite veins Rb, Rb/Ba and Rb/Sr increase and Ba, Sr, K/Rb and Ba/Sr decrease in K-feldspar, and Rb increases and Sr decreases in albite from aplite to coexisting pegmatite. Equilibrium was not attained for trace elements between coexisting feldspars.
3
Viegas, Gustavo, Luca Menegon, and Carlos Archanjo. "Brittle grain-size reduction of feldspar, phase mixing and strain localization in granitoids at mid-crustal conditions (Pernambuco shear zone, NE Brazil)." Solid Earth 7, no. 2 (March 9, 2016): 375–96. http://dx.doi.org/10.5194/se-7-375-2016.
Повний текст джерелаАнотація:
Abstract. The Pernambuco shear zone (northeastern Brazil) is a large-scale strike-slip fault that, in its eastern segment, deforms granitoids at mid-crustal conditions. Initially coarse-grained (> 50 µm) feldspar porphyroclasts are intensively fractured and reduced to an ultrafine-grained mixture consisting of plagioclase and K-feldspar grains (< 15 µm) localized in C' shear bands. Detailed microstructural observations and electron backscatter diffraction (EBSD) analysis do not show evidence of intracrystalline plasticity in feldspar porphyroclasts and/or fluid-assisted replacement reactions. Quartz occurs either as thick (∼ 1–2 mm) monomineralic veins transposed along the shear zone foliation or as thin ribbons ( ≤ 25 µm width) dispersed in the feldspathic mixture. The microstructure and c axis crystallographic-preferred orientation are similar in the thick monomineralic veins and in the thin ribbons, and they suggest dominant subgrain rotation recrystallization and activity of prism < a > and rhomb < a > slip systems. However, the grain size in monophase recrystallized domains decreases when moving from the quartz monomineralic veins to the thin ribbons embedded in the feldspathic C' bands (14 µm vs. 5 µm respectively). The fine-grained feldspar mixture has a weak crystallographic-preferred orientation interpreted as the result of shear zone parallel-oriented growth during diffusion creep, as well as the same composition as the fractured porphyroclasts, suggesting that it generated by mechanical fragmentation of rigid porphyroclasts with a negligible role of chemical disequilibrium. Once C' shear bands were generated and underwent viscous deformation at constant stress conditions, the polyphase feldspathic aggregate would have deformed at a strain rate 1 order of magnitude faster than the monophase quartz monomineralic veins, as evidenced by applying experimentally and theoretically calibrated flow laws for dislocation creep in quartz and diffusion creep in feldspar. Overall, our data set indicates that feldspar underwent a brittle-viscous transition while quartz was deforming via crystal plasticity. The resulting rock microstructure consists of a two-phase rheological mixture (fine-grained feldspars and recrystallized quartz) in which the polyphase feldspathic material localized much of the strain. Extensive grain-size reduction and weakening of feldspars is attained in the East Pernambuco mylonites mainly via fracturing which would trigger a switch to diffusion creep and strain localization without a prominent role of metamorphic reactions.
4
Sutarto, Sutarto, Arifudin Idrus, Sapto Putranto, Agung Harjoko, Lucas D. Setijadji, Franz M. Meyer, and Rama Danny. "HYDROTHERMAL ALTERATION AND VEIN TYPES OF THE RANDU KUNING PORPHYRY Cu-Au DEPOSIT AT SELOGIRI AREA, WONOGIRI." Buletin Sumber Daya Geologi 9, no. 1 (May 8, 2014): 48–61. http://dx.doi.org/10.47599/bsdg.v9i1.121.
Повний текст джерелаАнотація:
Many Tertiary hydrothermal altered dioritic composition intrusive rocks were found at the Randu Kuning area and its vicinity, Selogiri, including hornblende microdiorite, hornblende-pyroxene diorite and quartz diorite. The hydrothermal fluids which responsible for the alteration and mineralization at the area is associated with the occurence of the horblende microdiorite intrusion. The alteration zone at the Randu Kuning area and its vicinity can be divided intoseveral hydrothermal alteration zones, such as potassic (magnetite-biotite-K feldspar), prophyllitic (chlorite-magnetite-epidote-carbonate), phyllic (quartz-sericite-chlorite) and argillic (clay mineral-sericite). The alteration pattern in the Randu Kuning porphyry Cu-Au deposit is tipically a diorite model characterising by the domination of potassic alteration and prophyllitic zone. Phyllic and argillic alteration types are restrictive found within the fault zones. A lot of porphyry vein types were found and observed at the Randu Kuning area, and classified into at least seven vein types. The paragenetic sequence of those veins from theearliest to the latest respectively are 1). Magnetite-chalcopyrite±quartz-biotite veinlets, 2). Quartz±magnetite (A type) veins, 3). Banded/Laminated quartz-magnetite (M type) veins, 4). Quartz±K feldspar (B type)veins, 5). Quartz with thin centre line sulphide (AB type) veins, 6). Pyrite±chalcopyrite (C type) veinlets, and 7). Pyrite-quartz+chalcopyrire+carbonate (D type) veins. Gold and copper mineralisation of the Randu Kuning Porphyry Cu-Au deposit, mostly related to the presence of quartz veins/veinlets containing sulfide i.e. Quartz with thin centre line sulphide veins, Pyrite±chalcopyrite veinlets, and Pyrite-quartz+chalcopyrire+carbonate veins.
5
RAO, A. BHASKARA. "Silica enrichment, graphic granite and aquamarine growth: a new exploration guide." Anais da Academia Brasileira de Ciências 74, no. 3 (September 2002): 533–38. http://dx.doi.org/10.1590/s0001-37652002000300014.
Повний текст джерелаАнотація:
Granitic pegmatites are traditionally known to contain graphic, perthitic and myrmekitic intergrowths related to quartz and K- and Na- feldspars. They are further considered to characterise the pegmatite types distinguishing them from the granites and other related plutonic rock types. Graphic granite is accepted also as a synonym to granitic pegmatite. Systematic studies, by the author and colleagues, on the granitic pegmatite gem deposits have permitted the definition of two aquamarine gem provinces in ENE Brazil, one in the NeoProterozoic and the other in the Archaean sequences. Potash feldspars in the pegmatites in the former show perthitic intergrowths, whereas in the latter graphic intergrowth dominates with anomalously coarse centimetric quartz along the cleavages of K-feldspar. Several granitic pegmatites hosted in Archaean complex, in Lages Pintadas Aquamarine Province, Santa Cruz, RN State, present this texture-structure. Graphic intergrowth is attributed to the eutectic crystallization, succeeded by hydrothermal fluids with silica enrichment permitting the growth through diffusion and nucleation of quartz and along cleavages of potash feldspar. In the Archaean terrain, the abundance of recycled chert forming metapsammitic migmatites traversed by numerous quartz veins and coarse graphic granites, has contributed to the growth of beryl and also the aquamarines.
6
Schrijver, K., E. Marcoux, G. Beaudoin, and J. Y. Calvez. "Pb–Zn occurrences and their Pb-isotopic signatures bearing on metallogeny and mineral exploration—Paleozoic sedimentary rocks, northern Appalachians, Quebec." Canadian Journal of Earth Sciences 25, no. 11 (November 1, 1988): 1777–90. http://dx.doi.org/10.1139/e88-168.
Повний текст джерелаАнотація:
Galena Pb-isotope ratios of epithermal vein and disseminated sulfide occurrences in the Taconian Orogen and Siluro-Devonian basin cluster around 17.90–18.05 for 206Pb/204Pb and 37.70–38.00 for 208Pb/204Pb. The major source of Pb in most, if not all, occurrences is a fairly common continental crust, a characteristic found in published analyses of Grenville feldspar Pb. A southwest to northeast increase in galena 206Pb/204Pb ratios is ascribed to the supply of several types of detritus from Grenville basement during the Cambro-Ordovician: coarse-grained, K-feldspar-bearing in the southwest, grading into fine-grained phyllitic, and relatively more highly radiogenic in the northeast.Emplacement (i) of Pb–Zn–barite veins and disseminations, commonly of homogeneous crustal Pb-isotopic signature, was late Taconian; (ii) of Pb–Zn–quartz veins, of less homogeneous signature, was post-Taconian; and (iii) of Pb–Zn–carbonate veins, relatively highly radiogenic and commonly homogeneous, was late or post-Acadian. Signatures of the first-mentioned group seem to be most useful in exploration.
7
Willan, Robert C. R. "Structural setting and timing of hydrothermal veins and breccias on Hurd Peninsula, South Shetland Islands: a possible volcanic-related epithermal system in deformed turbidites." Geological Magazine 131, no. 4 (July 1994): 465–83. http://dx.doi.org/10.1017/s0016756800012103.
Повний текст джерелаАнотація:
AbstractQuartz veins and vein-breccias in a greywacke-shale sequence of ?Carboniferous-Triassic age were previously regarded as mesothermal silicified fault breccias, and related to an adjacent Eocene granodiorite pluton. New mapping of vein assemblages and textures, and their structural and cross-cutting relationships, demonstrates that the steeply dipping, sheeted, epithermal-textured vein array was hydraulic in origin and possibly Cretaceous in age. The main vein and breccia swarm trends for 14 km NNE along-strike and 2 km across-strike, cutting large irregular areas of silicified and brecciated sandstone, and patchy areas of pyritic, propylitic and K-feldspar alteration. Angular vein fabrics and hydraulic disruption textures indicate wedging by hydrothermal solutions, hydraulic rupture, brecciation and fragment transport, followed by open-space precipitation, in veins generally < 15 cm thick and breccias up to a few metres thick. Hydrothermal quartz, chlorite, calcite and chalcedony predominate, with variable amounts of chalcopyrite, galena, sphalerite and pyrite. Epidote, arsenopyrite, K-feldspar and andradite garnet are conspicuous in places. Breccias were pre-and syn-mineralization, whereas mineral precipitation was pre-, syn- and post-breccia formation. Hydrothermal activity was simultaneous with extensional faulting, striking NNE, and accompanied by intrusion of dacitic dykes. There followed conjugate shearing on east- and ESE-striking faults, intrusion of high-level tonalite stocks, and several phases of basaltic andesite dyke intrusion. These hypabyssal rocks were probably coeval with the Antarctic Peninsula Volcanic Group dominating Livingston Island, dated between 130 and 75 Ma. Minor copper and iron sulphide-bearing veins occur in adjacent volcanic and hypabyssal intrusive rocks. The Hurd Peninsula veins may, therefore, form part of a volcanic-epithermal hydrothermal system (adularia-sericite-quartz type), of Cretaceous age, rather than a porphyry-related system of Eocene age.
8
Dunkel, Kristina G., Luiz F. G. Morales, and Bjørn Jamtveit. "Pristine microstructures in pseudotachylytes formed in dry lower crust, Lofoten, Norway." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 379, no. 2193 (February 2021): 20190423. http://dx.doi.org/10.1098/rsta.2019.0423.
Повний текст джерелаАнотація:
Feldspar-rich pseudotachylytes from the island of Moskenesøya, Lofoten, formed in dry granulites under lower crustal conditions during the Caledonian orogeny. The central parts of the pseudotachylytes, where the cooling rates were slowest, are characterized by microlites and spherulites of plagioclase and K-feldspar. K-feldspar surrounding plagioclase is consistent with crystallization from a melt during cooling instead of devitrification as the origin of the spherulites. Very thin (a few micrometres wide) injection veins, which experienced very rapid quenching, contain amorphous or cryptocrystalline material. The preservation of this material and of the fine-grained microstructures shows that, under fluid-absent conditions, recrystallization and reactions are slow and the original microstructures of the pseudotachylytes can be preserved. This article is part of a discussion meeting issue ‘Understanding earthquakes using the geological record’.
9
Byrne, Kevin, Guillaume Lesage, Sarah A. Gleeson, Stephen J. Piercey, Philip Lypaczewski, and Kurt Kyser. "Linking Mineralogy to Lithogeochemistry in the Highland Valley Copper District: Implications for Porphyry Copper Footprints." Economic Geology 115, no. 4 (June 1, 2020): 871–901. http://dx.doi.org/10.5382/econgeo.4733.
Повний текст джерелаАнотація:
Abstract The Highland Valley Copper porphyry deposits, hosted in the Late Triassic Guichon Creek batholith in the Canadian Cordillera, are unusual in that some of them formed at depths of at least 4 to 5 km in cogenetic host rocks. Enrichments in ore and pathfinder elements are generally limited to a few hundred meters beyond the pit areas, and the peripheral alteration is restricted to narrow (1–3 cm) halos around a low density of prehnite and/or epidote veinlets. It is, therefore, challenging to recognize the alteration footprint peripheral to the porphyry Cu systems. Here, we document a workflow to maximize the use of lithogeochemical data in measuring changes in mineralogy and material transfer related to porphyry formation by linking whole-rock analyses to observed alteration mineralogy at the hand specimen and deposit scale. Alteration facies and domains were determined from mapping, feldspar staining, and shortwave infrared imaging and include (1) K-feldspar halos (potassic alteration), (2) epidote veins with K-feldspar–destructive albite halos (sodic-calcic alteration), (3) quartz and coarse-grained muscovite veins and halos and fine-grained white-mica–chlorite veins and halos (white-mica–chlorite alteration), and two subfacies of propylitic alteration comprising (4) prehnite veinlets with white-mica–chlorite-prehnite halos, and (5) veins of epidote ± prehnite with halos of chlorite and patchy K-feldspar. Well-developed, feldspar-destructive, white-mica alteration is indicated by (2[Ca-C] + N + K)/Al values <0.85, depletion in CaO and Na2O, enrichment in K2O, and localized SiO2 addition and is spatially limited to within ~200 m of porphyry Cu mineralization. Localized K2O, Fe2O3, and depletion in Cu, and some enrichment in Na2O and CaO, occurs in sodic-calcic domains that form a large (~34 km2) nonconcentric footprint outboard of well-mineralized and proximal zones enriched in K. Water and magmatic CO2-rich propylitic and sodic-calcic–altered rocks form the largest lithogeochemical footprint to the mineralization in the Highland Valley Copper district (~60 km2). Calcite in the footprint is interpreted to have formed via phase separation of CO2 from a late-stage magmatic volatile phase. Several observations from this study are transferable to other porphyry systems and have implications for porphyry Cu exploration. Feldspar staining and shortwave infrared imaging highlight weak and cryptic alteration that did not cause sufficient material transfer to be confidently distinguished from protolith lithogeochemical compositions. Prehnite can be a key mineral phase in propylitic alteration related to porphyry genesis, and its presence can be predicted based on host-rock composition. Sodic-calcic alteration depletes the protolith in Fe (and magnetite) and, therefore, will impact petrophysical and geophysical characteristics of the system. Whole-rock loss on ignition and C and S analyses can be used to map enrichment in water and CO2 in altered rocks, and together these form a large porphyry footprint that extends beyond domains of enrichment in ore and pathfinder elements and of pronounced alkali metasomatism.
10
Viegas, G., L. Menegon, and C. J. Archanjo. "Brittle grain size reduction of feldspar, phase mixing and strain localization in granitoids at mid-crustal conditions (Pernambuco shear zone, NE Brazil)." Solid Earth Discussions 7, no. 4 (October 30, 2015): 2953–98. http://dx.doi.org/10.5194/sed-7-2953-2015.
Повний текст джерелаАнотація:
Abstract. The Pernambuco shear zone (northeastern Brazil) is a large-scale strike-slip fault that, in its eastern segment, deforms granitoids at mid-crustal conditions. Initially coarse (> 50 μm) grained feldspar porphyroclasts are intensively fractured and reduced to an ultrafine-grained mixture consisting of plagioclase and K-feldspar grains (~ < 15 μm in size) localized in C' shear bands. Detailed microstructural observations and EBSD analysis do not show evidence of intracrystalline plasticity in feldspar porphyroclasts and/or fluid-assisted replacement reactions. Quartz occurs either as thick (~ 1–2 mm) monomineralic bands or as thin ribbons dispersed in the feldspathic mixture. The microstructure and c axis crystallographic preferred orientation are similar in the thick monomineralic band and in the thin ribbons, and suggest dominant subgrain rotation recrystallization and activity of prism ⟨a⟩ and rhomb ⟨a⟩ slip systems. However, the grain size in monophase recrystallized domains decreases when moving from the transposed veins to the thin ribbons embedded in the feldspathic C' bands (14 μm vs. 5 μm, respectively). The fine-grained feldspar mixture has a weak crystallographic preferred orientation interpreted as the result of oriented growth during diffusion creep, as well as the same composition as the fractured porphyroclasts, suggesting that it generated by mechanical fragmentation of rigid porphyroclasts with a negligible role of chemical disequilibrium. Assuming that the C' shear bands deformed under constant stress conditions, the polyphase feldspathic aggregate would have deformed at a strain rate one order of magnitude faster than the monophase quartz ribbons. Overall, our dataset indicates that feldspar underwent a brittle-viscous transition while quartz was deforming via crystal plasticity. The resulting rock microstructure consists of a two-phase rheological mixture (fine-grained feldspars and recrystallized quartz) in which the polyphase feldspathic material localized much of the strain. Extensive grain-size reduction and weakening of feldspars is attained in the East Pernambuco mylonites mainly via fracturing under relatively fluid-absent conditions which would trigger a switch to diffusion creep and further strain localization without a prominent role of metamorphic reactions.
11
Иванова, Ю. А., and Е. А. Власов. "Rutile K-feldspar-quartz veins of headwaters of the river Dvoynaya, Western Chukotka." Новые данные о минералах, no. 2018(52) (June 15, 2018): 40–42. http://dx.doi.org/10.25993/fm.2018.52.23626.
Повний текст джерелаАнотація:
Московский государственный университет им. М.В. Ломоносова, геологический факультет В вулканитах тытыльвеемской свиты встречены многочисленные прожилки и жилы кальцит-адуляркварцевого состава с титанитом, эпидотом, алланитом-(Се), датолитом, пренитом, хлоритом, светлой слюдой, сульфидами (пирит, халькопирит и молибденит), вольфрамитом, шеелитом и рутилом. В рутиле были определены примеси W6+, Nb5+, Fe3+, V3+ и Cr3+. Установлена прямая корреляция концентрации в рутиле W6+ и Nb5+ с суммой трехвалентных катионов, предложены следующие схемы изоморфного замещения: 3Ti4+ = W6+ + 2Me3+, 2Ti4+ = Nb5+ + Me3+. В ряде анализов рутила отмечается избыток трехвалентных катионов, не скомпенсированных высоковалентными примесями. Избыток трехвалентных катионов объясняется появлением в структуре анионных вакансий по схеме 2Ti4+ + O2– = 2Me3+ + [vac]. Данное предположение подтверждается дефицитом кислорода в ряде кристаллохимических формул рутила.
12
Xia, Qiong-Xia, Peng Gao, Guang Yang, Yong-Fei Zheng, Zi-Fu Zhao, Wan-Cai Li, and Xu Luo. "The Origin of Garnets in Anatectic Rocks from the Eastern Himalayan Syntaxis, Southeastern Tibet: Constraints from Major and Trace Element Zoning and Phase Equilibrium Relationships." Journal of Petrology 60, no. 11 (November 1, 2019): 2241–80. http://dx.doi.org/10.1093/petrology/egaa009.
Повний текст джерелаАнотація:
Abstract Amphibolite- and granulite-facies metamorphic rocks are common in the eastern Himalayan syntaxis of southeastern Tibet. These rocks are composed mainly of gneiss, amphibolite and schist that underwent various degrees of migmatization to produce leucogranites, pegmatites and felsic veins. Zircon U–Pb dating of biotite gneiss, leucocratic vein and vein granite from the syntaxis yields consistent ages of ∼49 Ma, indicating crustal anatexis during continental collision between India and Asia. Garnets in these rocks are categorized into peritecitc and anatectic varieties based on their mode of occurrence, mineral inclusions and major- and trace-element zoning. The peritectic garnets mainly occur in the biotite gneiss (mesosome layer) and leucocratic veins. They are anhedral and contain abundant mineral inclusions such as high-Ti biotites and quartz, and show almost homogeneous major-element compositions (except Ca) and decreasing HREE contents from core to rim, indicating growth during the P- and T-increasing anatexis. Peak anatectic conditions at 760–800°C and 9–10·5 kbar are well constrained by phase equilibrium calculations, mineral assemblages, and garnet isopleths. In contrast, anatectic garnets only occur in the vein granite. They are round or subhedral, contain quartz inclusions, and exhibit increasing spessartine and trace-element contents from core to rim. The garnet–biotite geothermometry and the garnet–biotite–plagioclase–quartz geobarometry suggest that the anatectic garnets crystallized at ∼620–650°C and 4–5 kbar. Some garnet grains show two-stage zoning in major and trace elements, with the core similar to the peritectic garnet but the rim similar to the anatectic garnet. Mineralogy, whole-rock major- and trace-element compositions and zircon O isotopes indicate that the two types of leucosomes were produced by hydration (water-present) melting and dehydration (water-absent) melting, respectively. The leucocratic veins contain peritectic garnet but no K-feldspar, have lower whole-rock K2O contents and Rb/Sr ratios, higher whole-rock CaO contents and Sr/Ba ratios, and show homogeneous δ18O values that are lower than those of relict zircons, indicating that such veins were produced by the hydration melting. In contrast, the vein granite contains peritectic garnet and K-feldspar, has higher whole-rock K2O contents and Rb/Sr ratios, lower whole-rock CaO contents and Sr/Ba ratios, and shows comparable δ18O values with those of relict zircons, suggesting that this granite were generated by the dehydration melting. Accordingly, both hydration and dehydration melting mechanisms have occurred in the eastern Himalayan syntaxis.
13
McNeil, A. M., and R. Kerrich. "Archean lamprophyre dykes and gold mineralization, Matheson, Ontario: the conjunction of LILE-enriched mafic magmas, deep crustal structures, and Au concentration." Canadian Journal of Earth Sciences 23, no. 3 (March 1, 1986): 324–43. http://dx.doi.org/10.1139/e86-035.
Повний текст джерелаАнотація:
At the Canadian Arrow deposit, Matheson, separate base- and precious-metal-bearing fracture arrays are associated with a trondhjemitic stock transected by lamprophyre dykes. Peripheral to the stock, high-Fe tholeiitic pillow basalts (Fe2O3 17.8 wt.%, TiO2 2.4 wt.%, Al2O3/TiO2 = 13.7), with interbedded felsic units, experienced amphibolite-facies hydrothermal or regional metamorphism and intense ductile deformation focussed within mylonite zones at the interflow horizons. The trondhjemite stock experienced pervasive reaction with marine water at temperatures that diminished to ≤ 150 °C: this was accompanied by conversion of plagioclase of igneous origin to albite, concomitant enrichment of sodium (Na2O = 8.32 ± 1.16 wt.%, 1σ), and shifts of albite up to δ18O = 14, with attendent, variably negative, quartz–albite fractionations.Galena-dominated veins were precipitated at 220–255 °C from hypersaline CaCl2–NaCl hydrothermal fluids with 22–34 equivalent wt.% NaCl, δ18O = +0.6 to +2.5; these were of evolved marine origin. Later gold-bearing quartz veins formed during hydraulic fracturing under conditions where Pfluid ≥ σ3 + tensile strength. Alteration in vein selvages involved the reaction of albite (δ18O = 14) to K-feldspar (δ18O = 11.3), with gains of Si, K, Rb, Ba, CO2, and S from the hydrothermal fluids and concomitant losses of Fe, Mg, and Na. Volume dilatations were up to +56%. Hydrothermal fluids implicated in this vein array were at 320 ± 20 °C, possessed low salinity, δ18OH2O = 8 ± 0.5, and underwent transient effervescence of CO2; they were of metamorphic or magmatic origin. Coexisting K-feldspar and hematite signify higher aqueous K+/H+ and more oxidizing conditions of deposition than that of most Archean lode gold deposits.Lamprophyre dykes containing trondhjemitic xenoliths were injected along two major subparallel fracture systems showing the same geometry and orientation as the gold-bearing veins. The dykes possess the low SiO2 (39.6 wt.%) and elevated incompatible (P, Th, Zr, Hf, LREE) and mafic (Cr, Ni, Co) trace elements characteristic of calc-alkaline lamprophyres; they are thought to be mantle derivatives. The dykes feature chondrite-normalized troughs at Ta–Nb and Ti. Fe–Mg carbonates in the least-altered lamprophyric dykes (δ13C = −2.8 ± 0.6) may have been derived from a magmatic carbonate reservoir, whereas hydrothermal calcites associated with gold veins (δ13C = −3.2 to −4.6) are interpreted to represent donation of carbon from a uniform reservoir containing carbonate, magmatic C, and carbonaceous components.The conjunction of trondhjemitic and lamprophyric rocks with major structures and gold deposits is interpreted in terms of transcrustal fractures utilized as a conduit for high-Na magmas from the base of the crust, for alkalic magmas from the mantle, and for discharge of hydrothermal fluids from a metamorphic or magmatic reservoir.
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Asadi, Sina, Farid Moore, Alireza Zarasvandi, and Majid Khosrojerdi. "First report on the occurrence of CO2-bearing fluid inclusions in the Meiduk porphyry copper deposit, Iran: implications for mineralisation processes in a continental collision setting." Geologos 19, no. 4 (December 1, 2013): 301–20. http://dx.doi.org/10.2478/logos-2013-0019.
Повний текст джерелаАнотація:
Abstract Hydrothermal alteration of the Meiduk porphyry copper deposit, south of the Kerman Cenozoic magmatic arc and southeast of the central Iranian volcano-plutonic belt has resulted in three stages of mineralisation characterised by veins and veinlets. These are, from early to late: (1) quartz + K-feldspar + biotite + pyrite ± chalcopyrite ± pyrrhotite ± magnetite (early potassic alteration and type-A veins); (2) quartz + chalcopyrite + pyrite + bornite + pyrrhotite + K- -feldspar + biotite + magnetite (potassic-sericitic alteration and type-B veins); and (3) quartz + pyrite + chalcopyrite + sericite (sericitic alteration and type-C veins). Most ores were formed during stages 2 and 3. Three main types of fluid inclusions are distinguished based on petrographical, microthermometrical and laser Raman spectroscopy analyses, i.e. type I (three-phase aqueous inclusions), type II (three-phase liquid-carbonic inclusions) and type III (multi-phase solid inclusions). The fluid inclusions in quartz veins of the stages are mainly homogenised at 340-530°C (stage 1), 270-385°C (stage 2) and 214-350°C (stage 3), respectively, with salinities of 3.1-16 wt.% NaCl equivalent, 2.2-43 wt.% NaCl equivalent and 8.2-22.8 wt.% NaCl equivalent, respectively. The estimated trapping pressures are 97.9-123.6 MPa (3.7-4.6 km) in stage 1 and 62.5-86.1 MPa (2.3-3.1 km) in stage 2, respectively. These fluid inclusions are homogenised in different ways at similar temperatures, suggesting that fluid boiling took place in stages 2 and 3. The fluid system evolved from high-temperature, medium-salinity, high-pressure and CO2-rich to low-temperature, low-pressure, high-salinity and CO2-poor, with fluid boiling being the dominating mechanism, followed by input of meteoric water. CO2 escape may have been a factor in increasing activities of NaCl and S2- in the fluids, diminishing the oxidation of the fluids from stage 1 to 3. The result was precipitation of sulphides and trapping of multi-phase solid inclusions in hydrothermal quartz veins.
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Abdel Gawad, Ahmed E., Hassan Eliwa, Khaled G. Ali, Khalid Alsafi, Mamoru Murata, Masoud S. Salah, and Mohamed Y. Hanfi. "Cancer Risk Assessment and Geochemical Features of Granitoids at Nikeiba, Southeastern Desert, Egypt." Minerals 12, no. 5 (May 13, 2022): 621. http://dx.doi.org/10.3390/min12050621.
Повний текст джерелаАнотація:
Different rock types (syenogranite, alkali feldspar granite and quartz syenite intruded by microgranite dikes and quartz veins) were investigated in the Nikeiba region in Egypt. The main components of the studied intrusive rocks, comprised of granites and quartz syenite, are plagioclase, amphibole, biotite, quartz and K-feldspar in different proportions. Ground gamma ray measurements show that syenogranite, quartz syenite and microgranite dikes have the highest radioactivity (K, eU, eTh and their ratios) in comparison with alkali feldspar granite. Geochemically, syenogranite, alkali feldspar granite and quartz syenite are enriched with large-ion lithophile elements (LILE; Ba, Rb, Sr) and high field-strength elements (HFSE; Y, Zr and Nb), but have decreased Ce, reflecting their alkaline affinity. These rocks reveal calc–alkaline affinity, metaluminous characteristics, A-type granites and post-collision geochemical signatures, which indicates emplacement in within-plate environments under an extensional regime. U and Th are increased in syenogranite and quartz syenite, whereas alkali feldspar granite shows a marked decrease in U and Th. The highest average values of AU (131 ± 49 Bq·kg−1), ATh (164 ± 35) and AK (1402 ± 239) in the syenogranite samples are higher than the recommended worldwide average. The radioactivity levels found in the samples are the result of the alteration of radioactive carrying minerals found inside granite faults. The public’s radioactive risk from the radionuclides found in the investigated granitoid samples is estimated by calculating radiological risks. The excess lifetime cancer (ELCR) values exceed the permissible limit. Therefore, the granitoids are unsuitable for use as infrastructure materials.
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Baron, M., S. Hillier, C. M. Rice, K. Czapnik, and J. Parnell. "Fluids and hydrothermal alteration assemblages in a Devonian gold-bearing hot-spring system, Rhynie, Scotland." Transactions of the Royal Society of Edinburgh: Earth Sciences 94, no. 4 (December 2003): 309–24. http://dx.doi.org/10.1017/s0263593300000717.
Повний текст джерелаАнотація:
ABSTRACTHydrothermal alteration at Rhynie, Aberdeenshire, Scotland, is concentrated along a fault zone, which juxtaposes surface deposits and the mineralised feeder zone to the Rhynie hotspring system. Mineralisation consists of breccias and veins filled with quartz, chert, calcite, K-feldspar and pyrite. Associated pervasive alteration comprises a high-temperature K-feldsparquartz-illite facies (formed at 250–350°C), a medium-temperature mixed layered illite/smectitequartz-K-feldspar-chlorite-calcite facies (formed at 150–200°C) and a low-temperature mixed layered illite/smectite-chlorite-calcite facies (formed at 100 to +150°C). The fluids responsible for mineralisation were mainly moderate- to high-temperature (Th =91–360°C), low-salinity (<0·2 to 2·9 wt.% NaCl eq.) H2O-NaCl-heated meteoric fluids comparable to modern and ancient hot-spring systems. The migration of these fluids was mainly restricted to a major fault zone bounding the Devonian basin. Fluids responsible for mineralisation, alteration and cementation elsewhere in the basin were low-temperature (Th 57 to 161°C), low- to high-salinity (<0·2 to 18 wt.% NaCl eq.) H2O-NaCl fluids, which resemble basinal brines.
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Hassan, Kamaleldin M. "Trace elements and REE enrichment at Seboah Hill, SW Egypt." Mineralogia 49, no. 1-4 (December 1, 2018): 47–65. http://dx.doi.org/10.2478/mipo-2018-0007.
Повний текст джерелаАнотація:
Abstract Seboah Hill - a small body of peralkaline granite (< 0.1 km2) in south-western Egypt containing aegirine minerals ± magnesiohornblende ± riebeckite, cut by dikes of riebeckite-aegirine rhyolite, and exhibiting high radioactivity in veins of K-feldspar-aegirine-chalcedony-quartz ± trace hematite ± trace goethite was sampled and analyzed using inductively coupled plasma methods. Whole-rock chemical compositions of 5 granite, 3-rhyolitedike and 10 radioactive vein samples are presented. Of special significance is the enrichment of trace elements and rare earth elements (REE) in the radioactive veins. These include up to 6081 ppm Zr, 4252 ppm Ce, 1514 ppm Nd, 1433 ppm La, 1233 ppm Nb, 875 ppm Y, 388 ppm Pr, 350 ppm Th, 222 ppm Sm, 189 ppm Gd, 159 ppm Dy, 153 ppm Hf, 83 ppm Er, 76 ppm Yb and 58 ppm U. The chondrite-normalized patterns of REE in all samples show only limited variation and have negative europium (Eu) anomalies. These findings suggest that the sources of the REE are genetically related. Values of the Eu anomalies vary from 0.38-0.41 for the radioactive veins, 0.39-0.53 for the granite and 0.31-0.44 for the rhyolite dikes. Eu variations are consistent for different paragentic stages.
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Upton, B. G. J., A. A. Finch, and E. Słaby. "Megacrysts and salic xenoliths in Scottish alkali basalts: derivatives of deep crustal intrusions and small-melt fractions from the upper mantle." Mineralogical Magazine 73, no. 6 (December 2009): 943–56. http://dx.doi.org/10.1180/minmag.2009.073.6.943.
Повний текст джерелаАнотація:
AbstractCa-poor and typically Na-rich feldspar megacrysts are common associates of spinel lherzolitic and pyroxenitic xenoliths in Scottish alkalic basalts. Associated megacrysts and composite megacrysts and salic xenoliths include apatite, magnetite, zircon, biotite, Fe-rich pyroxene(s) and corundum. The salic xenoliths and related megacrysts are referred to collectively as the ‘anorthoclasite suite': the majority of the samples are inferred to derive from the disaggregation of coarse-grained, typically Na-rich, syenitic protoliths at depth. Rare occurrences of euhedral anorthoclase megacrysts, together with zircon dating, imply that the suite crystallized at, or very shortly before, their entrainment by the basaltic host magmas. Some evidence suggests that the anorthoclasite suite protoliths lie within ultramafic (pyroxenitic) domains in the deep crust. The latter are inferred to be pegmatites, crystallized from carbonated trachytic magmas with widely variable Ca, Na, K, Ba and trace-element contents, and to have ranged from metaluminous to peraluminous. Crystal zonation and resorption textures within the salic xenoliths imply that the crystallization of the parent magmas was complex. Confirmation of this comes from cathodoluminescence studies of the feldspars showing that early ('primary’) anorthoclases and potassian albites exhibit partial replacement by a more potassic feldspar. A third generation of potassic feldspar (enriched in an assortment of trace elements and deduced to have crystallized from a carbonated high-K melt) forms transecting zoned veins in which carbonate fills the axial zone.Whereas most of the anorthoclasite suite materials are inferred to have grown from metaluminous magmas, the occurrence of magmatic corundum in salic xenoliths indicates crystallization from magmas that were peraluminous. The corundum-bearing samples also contain Nb-rich oxide minerals and their associated feldspars have the highest rare-earth element(REE)contents. Accordingly, the peraluminous trachyte magmas are deduced to have been specifically enriched in high field-strength trace elements. It is proposed that formation of the anorthoclasite suite protoliths is a phenomenon closely related to that of salic glass ‘pockets', well known from spinel lherzolite xenoliths around the world. Not only are there compositional affinities, but both sets of phenomena appear to have closely pre-empted the ascent of alkali basalt (host) magmas. We propose that the two sets of phenomena are linked and that the anorthoclasite suite derived from coarse-grained sheets, generated by the aggregation of salic melt fractions rising from the shallow mantle and heralding the onset of basaltic magmatism.
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Daneshvar, Narges, Hossein Azizi, Yoshihiro Asahara, Motohiro Tsuboi, and Mahdi Hosseini. "Rare Earth Elements and Sr Isotope Ratios of Large Apatite Crystals in Ghareh Bagh Mica Mine, NW Iran: Tracing for Petrogenesis and Mineralization." Minerals 10, no. 9 (September 22, 2020): 833. http://dx.doi.org/10.3390/min10090833.
Повний текст джерелаАнотація:
The 320 Ma Ghareh Bagh mica mine is the only active mica mine in northwest Iran, and hosts Mg-bearing biotite (phlogopite) with apatite, epidote, and calcite. Chemical investigation of apatite infers the high abundances of the rare earth elements (REEs up to 5619 ppm), higher ratios of the LREE/HREE ((La/Yb)N = 28.5–36.7)) and high content of Y (236–497 ppm). REE pattern in the apatite and host A-type granite is almost the same. Ghareh Bagh apatite formed from the early magmatic-hydrothermal exsolved fluids at the high temperature from the Ghushchi alkali feldspar granite. The apatite crystals came up as suspension grains and precipitated in the brecciated zone. The early magmatic-hydrothermal fluids settle phlogopite, epidote, chlorite, K-feldspar and albite down in the brecciation zone. Due to the precipitation of these minerals, the late-stage fluids with low contents of Na+, Ca2+ and REE affected the early stage of alteration minerals. The high ratios of 87Sr/86Sr (0.70917 to 0.70950) are more consistent with crustal sources for the apatite large crystals. The same ages (320 Ma) for both brecciated mica veins and host alkali feldspar granites infer the apatite and paragenesis minerals were related to host granite A-type granite in the Ghareh Bagh area.
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Leitch, Craig H. B., C. T. Hood, Xiao-Lin Cheng, and A. J. Sinclair. "Tip Top Hill volcanics: Late Cretaceous Kasalka Group rocks hosting Eocene epithermal base- and precious-metal veins at Owen Lake, west-central British Columbia." Canadian Journal of Earth Sciences 29, no. 5 (May 1, 1992): 854–64. http://dx.doi.org/10.1139/e92-073.
Повний текст джерелаАнотація:
Rocks hosting the Silver Queen epithermal Au–Ag–Zn–Pb–Cu vein deposit near Owen Lake, British Columbia, belong to the Tip Top Hill volcanics. They are lithologically similar to the informally named Upper Cretaceous Kasalka Group rocks exposed in the type area at Tahtsa Lake, 75 km southwest of the deposit, and at Mount Cronin, 100 km northwest of the deposit. The Kasalka Group rocks in the Tahtsa Lake area give questionable dates of 105 ± 5 Ma by K–Ar on whole rock but are cut by intrusions dated at 83.8 ± 2.8 Ma by K–Ar on biotite. The sequence at the Silver Queen deposit includes a polymictic conglomerate, followed upward by felsic fragmental rocks and a thick porphyritic andesite flow and sill unit, cut by microdiorite and quartz–feldspar porphyry intrusions. The porphyritic andesite and the microdiorite have been dated as Late Cretaceous (78.3 ± 2.7 and 78.7 ± 2.7 Ma, respectively, by K–Ar on whole rock), close to previous dates for these rocks (77.1 ± 2.7 and 75.3 ± 2.0 Ma, respectively). The quartz–feldspar porphyry intrudes the porphyritic andesites but has an older U–Pb zircon date of 84.6 ± 0.2 Ma, probably due to underestimation of the true age of the host rocks by the K–Ar whole-rock method. Later dykes correlate with younger volcanic rocks belonging to the Ootsa Lake and Endako groups. Eocene pre- and postmineral plagioclase-rich dykes (51.9 ± 1.8 to 51.3 ± 1.8 Ma) and late diabase dykes (50.4 ± 1.8 Ma; all by K–Ar on whole rock) may be correlative with trachyandesite volcanics of the Goosly Lake Formation, part of the Eocene Endako Group. These volcanics have been dated elsewhere at 55.6 ± 2.5 to 48.8 ± 1.8 Ma by K–Ar on whole rock and biotite, respectively. Mineralization at Silver Queen is therefore similar in age to, but slightly younger than, the producing Equity mine located 30 km to the northeast, which is estimated at 58.5 ± 2.0 Ma by K–Ar on whole rock.
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Mian, I., and M. J. Le Bas. "The biotite-phlogopite series in fenites from the Loe Shilman carbonatite complex, NW Pakistan." Mineralogical Magazine 51, no. 361 (September 1987): 397–408. http://dx.doi.org/10.1180/minmag.1987.051.361.06.
Повний текст джерелаАнотація:
AbstractThe Loe Shilman carbonatite sheet complex comprises an extensive amphibole sovite which is intruded by minor biotite sovite and amphibole ankeritic carbonatite. The carbonatites have fenitized the country rocks to form a metasomatic zone c. 100 m wide of alternating mafic and felsic mica-bearing banded fenites which grade into slates and phyllites. Phlogopite-rich micas occur nearest to the carbonatite contact. The biotites occur in K-feldspar + albite ± Na-amphibole ± aegirine and ± phengite fenites produced by the intrusion of the early amphibole sovite. Aegirine buffered the iron distribution and the biotites became more magnesian. Veins cross-cutting the fenites consist of biotite and/or Ba-bearing K-feldspar, and are interpreted to result from solutions emanating from the biotite sovite. The ankeritic carbonatite is responsible for the formation ofphlogopite in the fenites in a c. 3 m wide zone adjacent to the carbonatite, and evidently are the result of fenitizing fluids rich in Mg. Chemical equations calculated to balance the reactions interpreted to have taken place in the fenites suggest that about 10% of the Al and Si in the protolith was mobilized and moved towards the carbonatites during fenitization, and that the fenitizing solutions were strongly alkaline and oxidizing.
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Andrews, A. J., L. Owsiacki, R. Kerrich, and D. F. Strong. "The silver deposits at Cobalt and Gowganda, Ontario. I: Geology, petrography, and whole-rock geochemistry." Canadian Journal of Earth Sciences 23, no. 10 (October 1, 1986): 1480–506. http://dx.doi.org/10.1139/e86-143.
Повний текст джерелаАнотація:
The Ag–sulpharsenide vein deposits of northeastern Ontario occur along the north and northeastern margins of the Cobalt Embayment, a large irregular domain of Huronian-age clastic sediments intruded by Nipissing diabase sills and crosscut by regional-scale fault systems. The vein systems are mostly fault controlled, with mineralization always occurring adjacent to or within the diabase sills. Many of the mineralized structures crosscut the sills. All the economically productive deposits occur in close proximity to the Huronian–Archean unconformity where diabase sills and steeply dipping Archean volcanic sequences coincide.The vein systems show remarkable consistencies in their mineralogy, textures, and paragenesis. Their formation involved the precipitation of silicates (mainly quartz, chlorite, actinolite ± K-feldspar) during initial, limited dilation; this was followed by the introduction of significant quantities of carbonate (mainly calcite ± dolomite) during subsequent dilatant episodes. Most of the ore was precipitated during the silicate to carbonate transition. Wall-rock alteration haloes exhibit a silicate to carbonate paragenesis similar to that evident in the veins. Feldspathization is an important consequence of the alteration process, manifesting in the ubiquitous occurrence of albite in Nipissing diabase wall rocks and sporadic occurrences of K-feldspar in Archean basalt wall rocks.The mineralogy and chemistry of the veins and altered wall rocks indicate that CO2, Ca, Na, K, Ag, As, Co, Pb, rare earth elements, and in some cases Hg and Au were among the components introduced with the hydrothermal fluids. This was accompanied by significant net loss of Si, Fe, Mg, Zn, B, Li, and Sc from the wall rocks. The nature of the wall-rock alteration suggests that the mineralizing fluids were of high alkalinity and relatively low [Formula: see text]. They were not derived through lateral secretion but were introduced from a source remote from the immediate environment of ore deposition.Wall-rock alteration postdates the establishment of a low-temperature, regional alteration of the diabases and a chlorite spotting alteration in the Huronian sediments; the latter is a contact metamorphic effect accompanying diabase intrusion. These data indicate that Ag–sulpharsenide vein formation postdated intrusion of the diabases and much (possibly all) of their cooling histories.Collectively, our data discourage the theory that the Nipissing diabase sills acted purely as a heat and (or) fluid source in vein formation. A structural model is proposed in which the diabase sills acted as mechanically favourable sites for fracture generation during regional fault activity. This factor, together with the advent of boiling and (or) degassing of the mineralizing fluids at these specific sites are viewed as possible critical parameters mediating the localization and deposition of Ag–sulpharsenide ore. This model provides a reasonable explanation for the local and regional distribution of the deposits and appears to best satisfy all the geological, petrographic, and geochemical criteria.
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Galanopoulos, Evangelos, Panagiotis Voudouris, Constantinos Mavrogonatos, Paul Spry, Craig Hart, Vasilios Melfos, Federica Zaccarini, and Dimitrios Alfieris. "A New Porphyry Mo Mineralization at Aisymi-Leptokarya, South-Eastern Rhodope, North-East Greece: Geological and Mineralogical Constraints." Geosciences 8, no. 12 (November 24, 2018): 435. http://dx.doi.org/10.3390/geosciences8120435.
Повний текст джерелаАнотація:
A new porphyry Mo prospect has been discovered in the Aisymi-Leptokarya area, along the southern margin of the Byala Reka–Kechros metamorphic dome, south-eastern (SE) Rhodope metallogenic zone. The study area is dominated by an Oligocene felsic dike complex, which hosts the porphyry Mo mineralization and intrudes into upper Eocene sandstones-marls and the Leptokarya monzodiorite pluton. The Aisymi-Leptokarya felsic dike complex displays a rhyodacitic to dacitic composition with post-collisional affinities. The porphyry Mo mineralization occurs in the form of porphyry-style quartz stockworks in the felsic dike complex associated with potassic alteration characterized by hydrothermal K-feldspar. The ore minerals consist mainly of pyrite, molybdenite, kesterite, bismuthinite and galena within both the stockwork and the rock matrix. Bulk ore analyses indicate enrichment in Mo (up to 215 ppm), Se (up to 29 ppm), Bi (up to 8 ppm) and Sn (up to 14 ppm) in the porphyry quartz veins. Late-stage, north-east (NE-) and north-west (NW-)trending milky quartz intermediate-sulfidation epithermal veins with base metals, crosscut previous vein generations and are characterized by Ag, Sn and Te anomalies. The Aisymi-Leptokarya porphyry Mo prospect is set in a back-arc geotectonic regime and shares similarities to other post-subduction porphyry molybdenum deposits elsewhere.
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Shuaibu, A.M. and Ovwasa, M.O. "Petrography and Geochemistry of Bada’u and its Environ, Katsina State Northwestern Nigeria." International Journal of Science for Global Sustainability 5, no. 2 (December 24, 2019): 12. http://dx.doi.org/10.57233/ijsgs.v5i2.146.
Повний текст джерелаАнотація:
The systematic studies of petrography and geochemistry of Bada’u revealed that the area are underlain by crystalline rocks of the Basement Complex, which is categorized as the low grade schist belt. The mapped area is situated within Malumfashi Local Government area of Katsina State, part of Malumfashi sheet 79 NW, which lies between latitudes 11051ʹ0.00˝N to 110 55ʹ00˝N and longitude of 70 32ʹ0.00˝E to 7035ʹ0.00˝E. The rock units were mapped in the sub-area on a scale of 1:25,000, covering an area of about 40km2. The major lithological units mapped in the study area comprises basically of mica schist intercalated with quartzites, porphyritic granites, and minor lithology which includes granite-gneiss, gneiss. The study area shows the evidence of post and syn-Tectonic (Primary and Secondary) structures such as joints, fracture, zenolith, and quartz veins. The dominant joint trend and Quartz veins of the study area are N-S E-W directions respectively which follows the general trend of structures resulting from Pan-African Orogeny. Seven rock samples were collected for both petrography and geochemical studies (2 samples of granites, two samples of gneiss and three samples of mica schist). The major minerals observed under plane polarized and cross polarized light microscope of the granite-gneiss, mica schist and granites are Quartz, feldspar (orthoclase), and micaceous minerals (Biotite and Muscovite) respectively. The geochemical result shows that the rock units within the study area have high percentage of SiO2 and Al2O3 concentration in wt%. This suggest that the rocks within the study were formed from a silica rich source. The granite within the area are peraluminous and shows calc-alkaline characteristics, and occur in syn collision environment as revealed under various geochemical classification plots. The gneiss in the area also have high percentage of SiO2 and Al2O3, suggesting a calc-alkaline affinity. The lesser amount of Na2O against K2O reflect an abundance of K-feldspars rock forming silicate. The mica schist also has high percentage of SiO2 and Al2O3, the high aluminium enrichment in mica shcist reflects the control of their composition by aluminum clay minerals, the mica schist specifically has high Barium contents which indicate K – feldspar rich source rock. The chemical concentration of Rb is similar to their derivation from shales or metapelites, which is a reflection of their origin.
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Sekisova, V. S., S. Z. Smirnov, D. V. Kuzmin, A. Ya Shevko, and M. P. Gora. "Crust–Mantle Xenoliths from the Kharchinsky Volcano (Central Kamchatka Depression): Mineralogy and Petrogenesis." Russian Geology and Geophysics 62, no. 03 (March 1, 2021): 339–56. http://dx.doi.org/10.2113/rgg20194109.
Повний текст джерелаАнотація:
Abstract —We present results of a study of plutonic-rock xenoliths from the Kharchinsky Volcano (Central Kamchatka depression). The studied xenolith collection comprises nine samples of peridotites and clinopyroxenites. The peridotites are identified as wehrlites, dunites, and harzburgites composed of olivine, clino- and orthopyroxenes, amphibole, and chromite in varying amounts. The clinopyroxenites consist mostly of clinopyroxene and often contain subordinate olivine, amphibole, hercynite, and magnetite. The xenoliths have interstitial segregations and veins composed of chlorite, plagioclase, K-feldspar, orthopyroxene, barite, fluorapatite, ilmenite, and, more seldom, anhydrite, phlogopite, and some other minerals. The study has revealed that veinlet minerals sometimes replace primary minerals and form pseudomorphs, thus indicating the metasomatic origin of interstitial and vein mineral assemblages. The thermobarometric calculations for minerals have shown that peridotites formed at ~1140 °C and ≤10 kbar in the intermediate chambers at the depths from the spinel stability field to the Moho. Interstitial metasomatic alterations of rocks took place at ~400–850 °C.
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Bhatt, S. C., and Vinod K. Singh. "Neoarchean crustal shear zones and implications of shear indicators in tectonic evolution of Bundelkhand craton, central India." Journal of Geoscience, Engineering, Environment, and Technology 4, no. 2-2 (July 25, 2019): 11. http://dx.doi.org/10.25299/jgeet.2019.4.2-2.2125.
Повний текст джерелаАнотація:
The gneisses and granitoids emplaced along E-W sub-vertical crustal shear zones are represented as important tectonic units in Bundelkhand craton of central India. The tonalite-trondhjemite-granodiorite (TTG) gneisses (3.5-3.2 Ga; oldest unit), and streaky to mafic gneisses structurally deformed in D 1 deformation. The metabasic, felsic, banded iron formation and metasedimentaries of greenstone complex exposed in central part, have characteristics of three sets of folding (F 1 -F 3 ). These gneisses associated with migmatite, amphibolite, quartzite, and schist were evolved in D 2 compressive phase, which are not occurring in northern part of craton. The K-rich Neoarchean granitoids (2.6-2.49 Ga) were intruded as granitic complex (D 3 magmatic phase) and the E-W strike-slip Raksa-Garhmau shear zone reported as important tectonic unit, were evolved in asyn-to post-tectonic D 3 phase. The dolerite dykes (ca. 2.0 Ga) were emplaced along NW-SE fractures in extension setting during D 4 magmatic event. The NE-SW riedel shears occupied by giant quartz veins (reefs) evolved in Paleoproterozoic during D 5 endogenic activity.
The relationship between macro and microstructural fabrics has been documented within mylonitic foliation, stretching lineation, S-C planes and rotated fabrics, reflect mesoscopic shear indicators, as noted in three types of mylonitic rocks. i) The rotated porphyroclasts of quartz, feldspars and asymmetric pressure shadows showing strong undulose extinction, deformation lamellae, and dynamic recrystallization are characteristic features of protomylonite where altered orthoclase and kinked plagioclase are noticed. ii) Mylonite, a distinct mylonitic foliation represented by parallel orientation of elongated quartz and feldspar with flakes of mica. iii) The ground matrix of recrystallized quartz with few protoliths of quartz and feldspar are observed, important features of ultramylonite. The asymmetric microstructures viz. σa and σb mantled porphyroclasts, othermicrostructures show progressively deformed by crystal plastic (non-coaxial) strain softening under low to moderate temperature conditions. The sinistral top- to- SW sense of shear movement was dominant. The microfractures/ microfaults, kinking and pull apart structures observed in K- feldspars and are indicative of overprinting of brittle deformation on ductile shearing.
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Tsuruoka, Subaru, Thomas Monecke, and T. James Reynolds. "Evolution of the Magmatic-Hydrothermal System at the Santa Rita Porphyry Cu Deposit, New Mexico, USA: Importance of Intermediate-Density Fluids in Ore Formation." Economic Geology 116, no. 6 (September 1, 2021): 1267–84. http://dx.doi.org/10.5382/econgeo.4831.
Повний текст джерелаАнотація:
Abstract The Santa Rita porphyry Cu deposit in New Mexico, USA, is characterized by a stockwork of three vein types that differ in morphology, mineralogy, and associated alteration assemblages. Early quartz veins associated with potassic alteration are composed of recrystallized granular quartz grains that host ubiquitous hypersaline liquid and vapor-rich fluid inclusions. The early quartz likely formed at high (≳500°C) temperatures and lithostatic pressures. Hypogene Cu mineralization at Santa Rita is in sulfide veins that reopened or crosscut the early quartz veins. The sulfide veins are surrounded by alteration halos containing chlorite and K-feldspar. Rare quartz crystals are present in some of these chalcopyrite and pyrite veins. The cores of the quartz crystals contain hypersaline liquid and vapor-rich fluid inclusions, whereas the rims mostly contain hypersaline liquid inclusions. The quartz crystals are interpreted to have formed close to the ductile-brittle transition as a result of the pressure drop from lithostatic to hydrostatic conditions. Formation of the quartz crystals was postdated by the deposition of Cu sulfides. Grain boundaries between the quartz and the sulfide minerals are irregular in shape, with sulfide crosscutting growth zones in the quartz. The Cu sulfides are interpreted to have formed from intermediate-density fluids that form secondary fluid inclusion assemblages in all earlier-formed quartz types. Microthermometric investigations showed that these fluid inclusion assemblages homogenize at ~385° to 435°C by critical or near-critical behavior and have salinities of <10 wt % NaCl equiv. The precipitation of Cu sulfides occurred as a result of cooling of these fluids following their escape from the lithostatic into the hydrostatic realm. Retrograde quartz solubility caused the corrosion of earlier-formed quartz during Cu sulfide deposition. The youngest veins at Santa Rita are composed of quartz and pyrite. These veins are associated with intense sericite alteration that overprinted all earlier alteration assemblages. The late quartz hosts primary and secondary liquid-rich fluid inclusions, but no intermediate-density fluid inclusions were identified. This quartz vein type formed at temperatures <360°C and hydrostatic pressures. The paragenetic relationships show that hypogene Cu mineralization at Santa Rita postdated potassic alteration of the host rocks. The Cu mineralization was formed by cooling intermediate-density fluids with critical or near-critical densities as they escaped from lithostatic to hydrostatic conditions.
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Abdel Wanees, Nora G., Mohamed M. El-Sayed, Khalil I. Khalil, and Hossam A. Khamis. "Petrogenesis of contrasting magmatic suites in the Abu Kharif area, Northern Eastern Desert, Egypt: implications for Pan-African crustal evolution and tungsten mineralization." Geological Magazine 159, no. 3 (November 30, 2021): 441–67. http://dx.doi.org/10.1017/s0016756821001047.
Повний текст джерелаАнотація:
AbstractThe Abu Kharif area in the Northern Eastern Desert consists of contrasting granitic magma suites: a Cryogenian granodiorite suite (850–635 Ma), an Ediacaran monzogranite suite (635–541 Ma) and a Cambrian alkali riebeckite granite suite (541–485 Ma). Tungsten mineralization occurs within W-bearing quartz veins and a disseminated type confined to the monzogranite.Whole-rock geochemical data classify the granodiorite as a late-orogenic I-type with calc-alkaline affinity, while the monzogranite and alkali riebeckite granite represent respectively a post-orogenic highly fractionated I-type with calc-alkaline affinity and an anorogenic A1-subtype with alkaline affinity. Geochemical modelling indicates that the three intrusions represent separate magmatic pulses where the granodiorite was generated by ∼75 % batch partial melting of an amphibolitic source followed by fractional crystallization of hornblende, biotite, apatite and titanite. The monzogranite was formed by 62 % batch partial melting of the normal ‘non-metasomatized’ Pan-African crust of calc-alkaline granite composition followed by fractional crystallization of plagioclase, biotite, K-feldspar, magnetite, ilmenite, with minor apatite and titanite. The alkali riebeckite granite was generated by 65 % batch partial melting of metasomatized Pan-African granite source followed by fractional crystallization of plagioclase, K-feldspar, amphibole and biotite with minor magnetite, apatite and titanite. In general, the parent magmas of the three intrusions were originally enriched in W, but with different concentrations. This W-enrichment would be caused by magmatic-related hydrothermal volatile-rich fluids and concentrated within the monzogranite.
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Voudouris, Panagiotis, Vasilios Melfos, Constantinos Mavrogonatos, Alexandre Tarantola, Jens Gӧtze, Dimitrios Alfieris, Victoria Maneta, and Ioannis Psimis. "Amethyst Occurrences in Tertiary Volcanic Rocks of Greece: Mineralogical, Fluid Inclusion and Oxygen Isotope Constraints on Their Genesis." Minerals 8, no. 8 (July 28, 2018): 324. http://dx.doi.org/10.3390/min8080324.
Повний текст джерелаАнотація:
Epithermally altered volcanic rocks in Greece host amethyst-bearing veins in association with various silicates, carbonates, oxides and sulfides. Host rocks are Oligocene to Pleistocene calc-alkaline to shoshonitic lavas and pyroclastics of intermediate to acidic composition. The veins are integral parts of high to intermediate sulfidation epithermal mineralized centers in northern Greece (e.g., Kassiteres–Sapes, Kirki, Kornofolia/Soufli, Lesvos Island) and on Milos Island. Colloform–crustiform banding with alternations of amethyst, chalcedony and/or carbonates is a common characteristic of the studied amethyst-bearing veins. Hydrothermal alteration around the quartz veins includes sericitic, K-feldspar (adularia), propylitic and zeolitic types. Precipitation of amethyst took place from near-neutral to alkaline fluids, as indicated by the presence of various amounts of gangue adularia, calcite, zeolites, chlorite and smectite. Fluid inclusion data suggest that the studied amethyst was formed by hydrothermal fluids with relatively low temperatures (~200–250 °C) and low to moderate salinity (1–8 wt % NaCl equiv). A fluid cooling gradually from the external to the inner parts of the veins, possibly with subsequent boiling in an open system, is considered for the amethysts of Silver Hill in Sapes and Kassiteres. Amethysts from Kornofolia, Megala Therma, Kalogries and Chondro Vouno were formed by mixing of moderately saline hydrothermal fluids with low-salinity fluids at relatively lower temperatures indicating the presence of dilution processes and probably boiling in an open system. Stable isotope data point to mixing between magmatic and marine (and/or meteoric) waters and are consistent with the oxidizing conditions required for amethyst formation.
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Voudouris, P., I. Psimis, C. Mavrogonatos, C. Kanellopoulos, M. Kati, and E. Chlekou. "Amethyst occurrences in Tertiary volcanic rocks of Greece: mineralogical and genetic implications." Bulletin of the Geological Society of Greece 47, no. 1 (September 5, 2013): 477. http://dx.doi.org/10.12681/bgsg.11026.
Повний текст джерелаАнотація:
Epithermal-altered volcanic rocks in Greece host gem-quality amethyst veins in association with various silicates, carbonates, oxides, sulfides and halides. Host rocks are Oligocene to recent calc-alkaline to shoshonitic lavas and pyroclastics of intermediate- to acid composition. The amethyst-bearing veins occur in the periphery of porphyry-type and/or high-sulfidation epithermal mineralized centers in northern Greece (e.g. Sapes, Kirki, Kornofolia/Soufli, Lesvos island) and on Milos island in the active Aegean Volcanic Arc. Hydrothermal alteration around the quartz veins includes sericitic, K-feldspar (adularia), argillic, propylitic and zeolitic types. Precipitation of amethyst in the northern Greece occurrences, took place during the final stages of the magmatic-hydrothermal activity from near-neutral to alkaline fluids, as indicated by the presence of gangue adularia, calcite, smectite, chlorite, sericite, pyrite, zeolites (laumontite, heulandite, clinoptilolite), analcime and minor amounts of barite, halite, epidote and fluorite in the quartz veins. Amethyst at Milos Island (Chondro Vouno and Kalogries-Vani areas), is accompanied by barite, smectite and lepidocrocite. Colloform-crustiform banding with alternations of amethyst, chalcedony and/or carbonates is a common characteristic of the studied amethyst-bearing veins. Fluid inclusion- and mineralogical data suggest that the studied amethyst were formed at: 174-246 °C (Sapes area), 100-175 °C (Kirki and Kornofolia areas) and 223-234°C (Lesvos island). The amethyst formation requires oxidizing conditions and is probably the result of mixing between meteoric or seawater with upwelling hydrothermal fluids. The involvement of seawater in the studied mineralization is supported by the presence of halite and abundant barite in the veins. Finally, the studied amethyst deposits should be evaluated as potential gemstone sources in Greece.
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Chang, Jia, Jian-Wei Li, David Selby, Jia-Cheng Liu, and Xiao-Dong Deng. "Geological and Chronological Constraints on the Long-Lived Eocene Yulong Porphyry Cu-Mo Deposit, Eastern Tibet: Implications for the Lifespan of Giant Porphyry Cu Deposits." Economic Geology 112, no. 7 (November 1, 2017): 1719–46. http://dx.doi.org/10.5382/econgeo.2017.4527.
Повний текст джерелаАнотація:
Abstract The Yulong porphyry Cu-Mo deposit, the third largest porphyry Cu deposit in China, contains proven reserves of > 6.5 million metric tons (Mt) Cu and 0.4 Mt Mo. Previous radiometric dating studies have provided numerous ages for this deposit, but the timing and duration of the process governing the deposition of Cu and Mo remains not well constrained. In this paper, we first document multiple stages of mineralization and hydrothermal alteration associated with distinct magmatic pulses at Yulong by field and textural relationships, and then present high-precision molybdenite Re-Os ages of 14 quartz-molybdenite ± chalcopyrite veins representing these stages to precisely constrain the timing and duration of Cu-Mo mineralization. The ore-hosting Yulong composite stock consists of three successive porphyry intrusions: (1) monzonitic granite porphyry (MGP), (2) K-feldspar granite porphyry (KGP), and (3) quartz albite porphyry (QAP). The vein formation, Cu-Mo mineralization, and ore-related alteration are grouped into early, transitional, and late stages with respect to the intrusive history. The first two porphyry intrusions are followed by cyclical sequences of veining that are mainly associated with potassic alteration and have formed (1) ME vein/USTT, (2) EBE/T veins, (3) A1E/T veins, (4) A2E/BT veins, and (5) A3E/T veins. A2E/BT and A3E/T veins of the early and transitional stages are dominated by quartz and chalcopyrite ± pyrite, respectively, and represent the main Cu-Mo mineralization events. More than 80% of Cu and Mo at Yulong were deposited in the early stage with the remainder being formed in the transitional stage. The late-stage pyrite-quartz veins (DL), which are characterized by sericitic alteration halos, postdate the intrusion of QAP dikes and have no economic significance. Molybdenite Re-Os ages of A2E and BT veins indicate that sulfide deposition at Yulong was episodic over a prolonged history lasting over 5.13 ± 0.23 m.y. (1σ). However, the bulk Cu-Mo ores formed in a shorter time interval of 1.36 ± 0.24 m.y. (1σ) with most Cu precipitated in a more restricted timespan of 0.82 ± 0.24 m.y. (1σ) in the early stage. These results, combined with geochronologic data from porphyry copper deposits elsewhere, confirm that multiple magmatic-hydrothermal pulses with a lifespan of tens to hundreds of thousands of years are sufficient to form a giant porphyry copper deposit. Factors such as metal concentration, volume, and focusing efficiency of ore-forming fluids could have played important roles in producing a giant porphyry Cu deposit regardless of a short- or long-lived magmatic-hydrothermal system.
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Kerrich, R., D. F. Strong, A. J. Andrews, and L. Owsiacki. "The silver deposits at Cobalt and Gowganda, Ontario. III: Hydrothermal regimes and source reservoirs–evidence from H, O, C, and Sr isotopes and fluid inclusions." Canadian Journal of Earth Sciences 23, no. 10 (October 1, 1986): 1519–50. http://dx.doi.org/10.1139/e86-145.
Повний текст джерелаАнотація:
The Ag–, Co–Ni–sulpharsenide deposits of the Cobalt–Gowganda district are characterized by relatively uniform light-stable-isotope systematics, where δ18O in quartz spans 11.1–16.0‰; in K-feldspar, 10.1–12.3‰; in albite, 8.1–14.4‰; in actinolite, 6.0–7.6‰; in chlorite, 3.2–5.6‰; and δD in chlorite = −42 to −35‰. The temperature of hydrothermal silicate deposition was 150–230 °C, as calculated from Δquartz–chlorite, and triple to quadruple isotopic concordancy is locally preserved amongst quartz, chlorite, actinolite, and K-feldspar or albite. Filling temperature modes at 230 and 330 °C exist for primary inclusions in quartz and carbonates. Ore-forming hydrothermal fluids were isotopically characterized by δ18O = −2.5 to + 5‰, δD = −40 to + 5‰, interpreted to reflect isotopically and chemically evolved formation brines from Huronian aquifers, ultimately derived from marine pore fluids, and Proterozoic meteoric water recharge of the sedimentary basin. The restricted range of δ18Oquartz, Δquartz−chlorite, and δDchlorite from a large population of veins implies that the ore-forming fluids were tapped from a large reservoir, or reservoirs, relatively uniform with respect to temperature, δ18O, and δD.Quartzes in silicate selvages, wall rocks, and carbonate-dominated gangue are isotopically comparable, signifying fluid-dominated conditions and the initial precipitation of carbonates from fluids isotopically similar to those involved in the silicate stage and at comparable temperatures. Vein dolomites (δ18O = 21 to 23.1‰) continued to exchange down to temperatures of 110–140 °C in the presence of fluids where δ18O = 3 ± 2‰, during thermal attenuation of the ore-forming reservoir. Vein calcites (δ18O = 1.7 to 15.7‰) record late incursion of meteoric waters where δ18O = −8 to −22‰ at temperatures of ~50 °C. The population of vein carbonates clusters at δ13C = −3.1 to −5.3‰, and this is probably also close to the carbon-isotope signature of the hydrothermal fluid. The source of carbon is uncertain.Actinolites possess age-corrected 87Sr/86Sr = 0.715 to 0.729, for 2200 Ma, close to estimates for the contemporaneous Huronian ratio (0.7053–0.714) but more radiogenic than contemporaneous Archean volcanics (0.7017–0.7021) or the Nipissing diabase (0.7060–0.7061). On this basis, Sr is interpreted to have been derived principally from the Huronian sedimentary reservoir.Fluid inclusions in quartz and calcite of both mineralized and barren veins in the Cobalt and Gowganda mining camps and environs show five different types type I (L), type II (L + halite), type III (L + V), type IV (L + V + H), and type V (V), with types III and IV being most abundant. A histogram of all mine data shows modes around 100, 230, and 330 °C, with a range from > 560 to < 100 °C. No carbon dioxide was observed in the inclusions, although the dominance of calcite and dolomite in the veins attests to its presence during mineralization. Several samples show evidence of aqueous boiling, allowing a direct pressure determination of about 600 bar (60 MPa). The fluids were highly saline NaCl–CaCl2 brines, with up to 54 wt.% NaCl equivalent and highly variable Na/Ca ratios. Fluid inclusions in samples of barren veins from Lundy Township, outside the areas of known mineralization, do not appear to be significantly different from those of the mineralized veins, indicating that the hydrothermal fluids were active throughout a large area of the Huronian basin; this is corroborated by the disturbance of Pb- and Sr-isotope systems in the Nipissing, Huronian, and Archean.The Nipissing diabase likely served as a heat source to mobilize metals and advect formation brines, which may have derived the metals from either or all of the Huronian sediments or the Archean volcanics Nipissing diabase and sedimentary rocks. We suggest a genetic scheme for the veins involving CO2 effervescence and aqueous boiling inducing pH increase and thereby mediating rapid precipitation of ore minerals coeval with and followed by carbonates. This process explains most of the presently known major and minor characteristics of the vein systems and their host rocks, including the chloritic and sodic metasomatism of the Archean and Huronian rocks, abundant calcite, the compositional and mineralogical variability of the ore minerals, the textural variability of both the carbonates and ore minerals, the paragenetic sequence of alteration and mineralization, the distribution of ore minerals with respect to the diabase and other rocks, the relatively narrow vertical extent of mineralization, variations in ore grade and tonnage, and the distribution of economic deposits on the periphery of the Huronian basin.
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Sutarto, Sutarto, Arifudin Idrus, Agung Harijoko, Lucas Donny Setijadji, Franz Michael Meyer, Sven Sindern, and Sapto Putranto. "Hydrothermal Alteration and Mineralization of the Randu Kuning Porphyry Cu-Au and Intermediate Sulphidation Epithermal Au-Base Metals Deposits in Selogiri, Central Java, Indonesia." Journal of Applied Geology 1, no. 1 (July 26, 2016): 1. http://dx.doi.org/10.22146/jag.26951.
Повний текст джерелаАнотація:
The Randu Kuning Porphyry Cu-Au prospect area is situated in the Selogiri district, Wonogiri regency, Central Java, Indonesia, about 40 km to the South-East from Solo city, or approximately 70 km east of Yogyakarta city. The Randu Kuning area and its vicinity is a part of the East Java Southern Mountain Zone, mostly occupied by both plutonic and volcanic igneous rocks, volcaniclastic, silisiclastic and carbonate rocks. Magmatism-volcanism products were indicated by the abundant of igneous and volcaniclastic rocks of Mandalika and Semilir Formation. The Alteration zones distribution are generally controlled by the NE–SW and NW–SE trending structures. At least eight types of hydrothermal alteration at the Randu Kuning area and its vicinity had been identified, i.e. magnetite + biotite ± K-feldspar ± chlorite (potassic), chlorite + sericite + magnetite ± actinolite, chlorite + magnetite ± actinolite ± carbonate (inner propylitic), chlorite + epidote ± carbonate (outer propylitic), sericite + quartz + pyrite (phyllic), illite + kaolinite ± smectite (intermediate argillic), illite + kaolinite ± pyrophyllite ± alunite (advanced argillic) and quatz + chlorite (sillisic) zones. The Randu Kuning mineralization at Selogiri is co existing with the porphyry Cu-Au and intermediate sulphidation epithermal Au-base metals. Mineralization in the porphyry environment is mostly associated with the present of quartz-sulphides veins including AB, C, carbonate-sulphides veins (D vein) as well as disseminated sulphides. While in the epithermal prospect, mineralization is particularly associated with pyrite + sphalerite + chalcopyrite + carbonate ± galena veins as well as hydrothermal breccias. The Randu Kuning porphyry prospect has copper gold grade in range at about 0.66–5.7 gr/t Au and 0.04–1.24 % Cu, whereas in the intermediate sulphidation epithermal contain around 0.1–20.8 gr/t Au, 1.2–28.1 gr/t Ag, 0.05–0.9 % Zn, 0.14–0.59 % Pb and 0.01–0.65 % Cu.
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Fan, Gao-Hua, Jian-Wei Li, Xiao-Dong Deng, Wen-Sheng Gao, and Si-Yuan Li. "Age and Origin of the Dongping Au-Te Deposit in the North China Craton Revisited: Evidence from Paragenesis, Geochemistry, and In Situ U-Pb Geochronology of Garnet." Economic Geology 116, no. 4 (June 1, 2021): 963–85. http://dx.doi.org/10.5382/econgeo.4810.
Повний текст джерелаАнотація:
Abstract Dongping is the largest Au-Te vein deposit (~120 t Au) in the North China craton, but its age, origin, and setting remain unsolved. Here, we integrate paragenesis, geochemistry, and in situ U-Pb geochronology of garnet to constrain the timing and possible origin of the Dongping Au-Te deposit. Gold mineralization at Dongping is hosted in the Shuiquangou alkaline complex (ca. 401–390 Ma) and dominated by quartz-sulfide veins with minor ores in adjacent alteration envelopes. Andradite to grossular garnets are recognized in pre-, syn-, and post-ore quartz veins as well as mineralized alteration envelopes and are closely associated with a variety of ore and gangue minerals, mainly including K-feldspar, quartz, specularite, magnetite, pyrite, tellurides, epidote, and calcite. The paragenetic, textural, fluid inclusion, and compositional data suggest that garnets precipitated directly from a low-salinity fluid at 302° to 383°C and 90 to 330 bar. Garnets from various veins and alteration envelopes have similar U contents ranging from 0.80 to 13.89 mg/kg and yield reproducible U-Pb dates of 142 ± 5 to 139 ± 6 Ma (1σ) by laser ablation-inductively coupled plasmamass spectrometry. The dating results suggest that gold mineralization at Dongping occurred in the Early Cretaceous and thus preclude a genetic link between Au-Te mineralization and the ore-hosting alkaline intrusion as commonly suggested. When combined with independent geologic, geochemical, and geochronological studies, the new garnet U-Pb dates allow us to classify the Dongping Au-Te deposit as an oxidized intrusion-related gold deposit, with the causative magma likely derived from melting of an ancient enriched lithospheric mantle source due to destruction of the subcontinental lithospheric keel beneath the North China craton—a catastrophic event induced by the westward subduction of the Paleo-Pacific plate. This study highlights garnet U-Pb dating as a potential robust geochronometer for gold vein deposits elsewhere.
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Hassaan, Mahmoud M., Sayed A. Omar, Ahmed E. Khalil, Taher M. Shahin, Islam M. El-Naggar, M. I. Sayyed, and Mohamed Y. Hanfi. "Prognostic Exploration of U-F-Au-Mo-W Younger Granites for Geochemical Pathfinders, Genetic Affiliations, and Tectonic Setting in El-Erediya-El-Missikat Province, Eastern Desert, Egypt." Minerals 12, no. 5 (April 22, 2022): 518. http://dx.doi.org/10.3390/min12050518.
Повний текст джерелаАнотація:
Younger granite bodies form two arches, the western and the eastern (WA, EA), which extend from the south northwards from the Meatique, ophiolitic group-island arc rocks, to the large older granite outcrop to the north. This paper concerns the feasibility of exploration in the El-Erediya-Ria El-Garah-El-Gidami-El-Missikat Y Gr regions. Fieldwork and remote sensing, together with geochemical, petrochemical, and mineralogical studies, are used to show the controlling factors, routes, and the origins of the deposits. Remote sensing is used to delineate the different rock units. Normal and strike–slip NW, NNE faults, veins, fractured ENE shear zones, and alteration zones of magmatic-hydrothermal fluids are discussed. Granites are considered using petrochemical diagrams as resources. These rocks are categorized as syeno- and alkali feldspar granites. Geochemical binary relationships recognized the granites are highly fractionated calc-alkaline-altered Monzo-, syeno-, and alkali feldspar granites formed in the active continental margin. The observed positive Ga vs. Cu, Zn, and Ni correlations are used for epithermal-magmatic-hydrothermal polymetallic veins and mineralized greisen zones. Negative Cu vs. Mo correlation patterns show probable Mo-porphyry deposits in the deeper zones at the contact point between porphyritic perthite and perthite granitic El-Erediya mass. The Zr/Sr between 1.65 to 2.93 plus fluorites in El-Missikat and up to 5.48 plus fluorites in El-Erediya show both U-poor at El-Missikat and U-rich deposits at El-Erediya. The recorded U, Th, Cu, and Pb vertical zoning sequence of deposition differentiates U aureole and deposit zones. The estimated lateral zoning sequences of deposition of these elements define the centers of U deposits. Pathfinders for the deposit of the examined area include the positive Fe2O3 vs. Mg O and Fe2O3 vs. Ca O correlations, and also negative Rb/Sr vs. K/Na and Rb vs. Sr ones, can be applied to future prospecting for similar U-F-Au-W-Mo deposits in the Eastern Desert of Egypt.
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Kato, Satomi, and Sumio Miyashita. "Genesis of vesiculation in dolerite sills of the Shimokawa ophiolite in the northern Hidaka belt，Hokkaido and origin of albite - K-feldspar veins." Journal of the Geological Society of Japan 128, no. 1 (December 29, 2022): 427–43. http://dx.doi.org/10.5575/geosoc.2022.0039.
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Poutiainen, Matti. "Evolution of a metamorphic fluid during progressive metamorphism in the Joroinen-Sulkava area, southeastern Finland, as indicated by fluid inclusions." Mineralogical Magazine 54, no. 375 (June 1990): 207–18. http://dx.doi.org/10.1180/minmag.1990.054.375.07.
Повний текст джерелаАнотація:
AbstractFluid inclusions in the progressively metamorphosed rocks of the Joroinen-Sulkava area, located in the south-eastern end of the Raahe-Ladoga zone near the Archaean-Proterozoic boundary, southeastern Finland, fall into four main categories: (1) H2O-rich, (2) CO2-rich, (3) mixed H2O-CO2 and (4) CH4-N2 inclusions. The samples were collected from quartz veins associated with different deformation phases (D2-D4) and from metapelites. The progressive stage of metamorphism took place mainly during the D2 deformation. The age of metamorphism and D2 deformation becomes younger with increase in metamorphic grade from amphibolite to granulite facies.Regional distribution of the different fluid types indicates a change in fluid regime from H2O to CO2-dominant during the progressive stage of the metamorphism. H2O entered preferentially into the anatectic melt. The possibility of CO2 infiltration from deeper crust can not be excluded, because granulite facies rocks occur most probably below the lower grade zones. A zone enriched in CH4-N2 fluids is located near the lineament zones caused by the D3 deformation. This fluid type dominates the Au-bearing D2–D3 quartz lenses in the K-feldspar-sillimanite zone. Density data of early CO2 inclusions in combination with estimates of metamorphic temperatures (645–750°C) in the different metamorphic zones indicate a pressure range of 3.0–4.5 kbar, which is consistent with data derived from mineral geobarometry. The diversity of fluid types encountered in the D2–D4 quartz veins are a result of the passage of different fluids through veins at different times without re-equilibrating with the wall rocks. However, it is supposed that the CH4-N2 fluid is derived from a CO2-rich fluid with XCH4 ⩽ 0.4 by re-equilibration during its passage through the rocks.
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Dolníček, Zdeněk, Petr Stöhr, Jana Ulmanová, and Luboš Vrtiška. "Kausticky metamorfovaný pískovcový xenolit a doprovodná hydrotermální mineralizace z neovulkanitů od Prackovic nad Labem (České středohoří)." Bulletin Mineralogie Petrologie 30, no. 1 (2022): 95–107. http://dx.doi.org/10.46861/bmp.30.095.
Повний текст джерелаАнотація:
Technical workings realized near Prackovice nad Labem (České středohoří Mts., Czech Republic) yielded new findings about rocks and mineral veins present in Cenozoic volcanites. The studied xenolith represents a piece of pyrometamorphosed and hydrothermally altered sandstone enclosed in an alkaline basic volcanic rock. The core of the xenolith contains relicts of clasts of quartz, embedded in a matrix composed of laths of quartz (probably pseudomorphs of quartz after tridymite) and symplectitic intergrowths of alkali feldspar (sanidine Or57-81Ab19-41An0-1) and quartz. This core is rimmed by drusy overgrowths of sanidine and crystals of fluorapatite, aegirine-augite and titanite. All silicates are characterized by a significant substitution of Al by Fe3+, which is probably the result of high content of Fe3+ in the sandstone protolith (perhaps in limonite cement). The marginal part of xenolith is formed by zeolites (chabazite-K and phillipsite-K), saponite and calcite. These minerals likely crystallized at very low temperatures (<100 °C) in a vug, leaving after volatiles, which were expelled during pyrometamorphism of the xenolith. In addition, we have studied tiny hydrothermal veinlets hosted by neovolcanites, composed of a mixture of Al-rich phyllosilicates (probably a mineral from the kaolinite group and smectite) and strongly substituted carbonates including siderite (Sid55-91Mag3-38Cal5-31Rdc1) and calcite (Cal58-90 Mag8-41Sid1-6).
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Johnson, T. E., N. F. C. Hudson, and G. T. R. Droop. "Wollastonite-bearing assemblages from the Dalradian at Fraserburgh, northeast Scotland and their bearing on the emplacement of garnetiferous granitoid sheets." Mineralogical Magazine 64, no. 6 (December 2000): 1165–76. http://dx.doi.org/10.1180/002646100549959.
Повний текст джерелаАнотація:
AbstractMetasediments of the Tayvallich Subgroup of the Dalradian at Kinnairds Head, Fraserburgh are metamorphosed to sillimanite + K-feldspar grade and form part of the classic high-T low-P Buchan metamorphic terrain. Pelitic samples constrain peak-metamorphic conditions to 615±13°C and 2.2±0.2 kbar. At or close to the metamorphic peak, irregular garnetiferous aplites and autopegmatite bodies intruded the metasediments. Thin marble bands within the sequence are dominated by calcite with diopside, and equilibrated with relatively CO2-rich, internally buffered fluids. Where these are in close proximity to granitoid pegmatites, wollastonite dominates the matrix, and fractures and veins running through the rock contain concentrations of grossular and vesuvianite. With increasing distance from the pegmatite, vesuvianite and then grossular disappear, and wollastonite is only patchily developed. Such occurrences require a flushing of the marble by metasomatic (siliceous and aluminous) aqueous fluids which were derived from the de-watering of the adjacent pegmatite as it crystallized. The large quantities of dissolved silica led to pervasive wollastonite formation for several metres. The smaller quantities of Al reacted to form Ca-Al-silicates which were confined to the fractures.
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Milton, Jack E., Kenneth A. Hickey, Sarah A. Gleeson, Hendrik Falck, and Julien Allaz. "In Situ Monazite Dating of Sediment-Hosted Stratiform Copper Mineralization in the Redstone Copper Belt, Northwest Territories, Canada: Cupriferous Fluid Flow Late in the Evolution of a Neoproterozoic Sedimentary Basin." Economic Geology 112, no. 7 (November 1, 2017): 1773–806. http://dx.doi.org/10.5382/econgeo.2017.4529.
Повний текст джерелаАнотація:
Abstract The 300-km-long Redstone copper belt in the Mackenzie Mountains, Northwest Territories, Canada, is composed of a series of sediment-hosted stratiform copper (SSC) deposits hosted in Neoproterozoic fault-bounded intracontinental rift basins. Mineralization at Coates Lake, the largest of these deposits, is concentrated within microbial laminite layers in the transition zone between underlying continental red beds of the Redstone River Formation and overlying marine carbonates of the Coppercap Formation. Disseminated cupriferous sulfides (chalcopyrite, bornite, and chalcocite) form part of a late diagenetic mineral association with dolomite, K-feldspar, albite, quartz, monazite, apatite, and pyrite that partially replaced detrital and early diagenetic minerals, including calcite cements, sulfate, and earlier generations of pyrite. Bornite (± minor chalcopyrite), calcite, dolomite, quartz, K-feldspar, and albite were also deposited in rare bedding-parallel veins adjacent to the lowermost mineralized microbial laminite layer in the transition zone. The absolute timing of mineralization was constrained by in situ U-Th-Pb chemical dating of monazite from four samples hosting disseminated SSC-type mineralization. The monazite have rounded, Th-U-heavy rare earth element-rich, detrital cores surrounded by Th-U-poor, light rare earth element-S-Sr-rich rims. The rim stage of monazite growth is intergrown with and enveloped by cupriferous sulfide and is paragenetically constrained as being part of the disseminated SSC-type mineralizing event. Eleven detrital cores yielded dates between 1843 and 1025 Ma, older than the depositional age of transition zone strata previously constrained to be between 775 and 732 Ma. Ten monazite rims yielded dates between 661 and 607 Ma. A weighted average date of 635 ± 13 Ma provides a maximum estimate, and is our preferred interpretation, for the absolute age of all copper mineralization at the Coates Lake deposit. Mineralization formed approximately 100 m.y. after deposition of the host rocks, during the thermal sag phase of continental rifting. Stratigraphic reconstructions, coupled with estimates of sediment compaction, indicate that at 635 Ma the transition zone was buried by ~4 km of sediments and overlaid another ~1.7 km of sediments that formed the Redstone River and Thundercloud Formations. Mudstone and carbonate-rich units above the transition zone acted as low permeability caps that led to suprahydrostatic fluid pressures in the underlying sediments. The bedding-parallel veins indicate transient supralithostatic fluid pressures. Free convection of pore fluids began within the transition zone and underlying units once they became hydrologically isolated from overlying strata. Mineralization formed as oxidized saline pore fluids circulated through the red beds (± underlying basaltic flows and basal sedimentary detritus), stripping copper and carrying it up into the transition zone. The salinity of the pore fluids may have, at least in part, originated from cryogenic brines generated by the Sturtian (717–662 Ma) global glaciation event.
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Damdinova, Ludmila, and Bulat Damdinov. "Tungsten Ores of the Dzhida W-Mo Ore Field (Southwestern Transbaikalia, Russia): Mineral Composition and Physical-Chemical Conditions of Formation." Minerals 11, no. 7 (July 5, 2021): 725. http://dx.doi.org/10.3390/min11070725.
Повний текст джерелаАнотація:
This article discusses the peculiarities of mineral composition and a fluid inclusions (FIs further in the text) study of the Kholtoson W and Inkur W deposits located within the Dzhida W-Mo ore field (Southwestern Transbaikalia, Russia). The Mo mineralization spatially coincides with the apical part of the Pervomaisky stock (Pervomaisky deposit), and the W mineralization forms numerous quartz veins in the western part of the ore field (Kholtoson vein deposit) and the stockwork in the central part (Inkur stockwork deposit). The ore mineral composition is similar at both deposits. Quartz is the main gangue mineral; there are also present muscovite, K-feldspar, and carbonates. The main ore mineral of both deposits is hubnerite. In addition to hubnerite, at both deposits, more than 20 mineral species were identified; they include sulfides (pyrite, chalcopyrite, galena, sphalerite, bornite, etc.), sulfosalts (tetrahedrite, aikinite, stannite, etc.), oxides (scheelite, cassiterite), and tellurides (hessite). The results of mineralogical and fluid inclusions studies allowed us to conclude that the Inkur W and the Kholtoson W deposits were formed by the same hydrothermal fluids, related to the same ore-forming system. For both deposits, the fluid inclusion homogenization temperatures varied within the range ~195–344 °C. The presence of cogenetic liquid- and vapor-dominated inclusions in the quartz from the ores of the Kholtoson deposit allowed us to estimate the true temperature range of mineral formation as 413–350 °C. Ore deposition occurred under similar physical-chemical conditions, differing only in pressures of mineral formation. The main factors of hubnerite deposition from hydrothermal fluids were decreases in temperature.
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Biagioni, Cristian, Yves Moëlo, Natale Perchiazzi, Nicola Demitri, and Giovanni Lepore. "Lead–Antimony Sulfosalts from Tuscany (Italy). XXIV. Crystal Structure of Thallium-Bearing Chovanite, TlPb26(Sb,As)31S72O, from the Monte Arsiccio Mine, Apuan Alps." Minerals 8, no. 11 (November 18, 2018): 535. http://dx.doi.org/10.3390/min8110535.
Повний текст джерелаАнотація:
A thallium-bearing variety of the lead–antimony oxysulfosalt chovanite from the Monte Arsiccio mine (Apuan Alps, Tuscany, Italy) has been reexamined. It occurs as thin, ribbon-like crystals, black in color, up to 5 mm in length in vugs of dolomite ± baryte ± quartz veins embedded in the metadolostone of the Sant’Olga level. Associated minerals are rouxelite, robinsonite, sphalerite, valentinite, baryte, dolomite, quartz, and Ba-rich K-feldspar. Chemical analysis pointed to contents of Tl up to 0.86 apfu, corresponding to the ideal chemical formula TlPb26(Sb,As)31S72O. The structural role of thallium has been investigated using single-crystal X-ray diffraction using synchrotron radiation (λ = 0.59040 Å). Thallium-rich chovanite is monoclinic, space group P21/c, with unit-cell parameters a = 34.280(3), b = 8.2430(7), c = 48.457(4) Å, β = 106.290(4)°, and V = 13143(2) Å3. The crystal structure was refined to a final R1 = 0.083 for 12,052 reflections with Fo > 4σ(Fo) and 1210 refined parameters. The general features of thallium-rich chovanite agree with those of chovanite. Thallium is present as Tl+; it is disordered among two mixed (Pb/Tl) positions, with a Tl/Pb atomic ratio below 1, that precludes this compound to be a new species.
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Adeola, Adewole John, and Abisola M. Oyebola. "Mineralogy and Geochemistry of the Weathering Profiles above the Basement Rocks in Idi- Ayunre and Akure Districts, Southwestern Nigeria." Journal of Geography and Geology 8, no. 2 (March 16, 2016): 15. http://dx.doi.org/10.5539/jgg.v8n2p15.
Повний текст джерелаАнотація:
Idi-ayunre and Akure areas are part of the basement complex of southwestern Nigeria and are predominantly consisted of gneisses, granite and migmatite with some minor quartz veins and pegmatite. These rocks have been greatly weathered to form clay, laterite and soils.Chemical analysis were carried out on basement rocks and exposed profiles. The weathering profile was subjected to X ray diffraction (XRD) analysis to determine mineralogical compositions whereas Chemical Index of Alteration (CIA) was calculated from the elemental concentrated data.Weathering of basement rocks in Idi-Ayunre and Akure districts resulted in the formation of soil layer which ranged 0-0.4m, laterite layer 1.2-2.2m, and clayey zone 3.8-6.6m. Quartz, plagioclase, microcline, and biotite were the main minerals in parent rocks. Some of the primary minerals such as biotite and K-feldspar have been weathered to form kaolinite. Quartz, kaolinite and goethite formed the dominant minerals revealed by X-ray diffraction on decomposed granite sequences. The results from chemical analysis showed that Al and Fe have been enriched in weathering profiles of banded gneiss, migmatite gneiss and porphyritic granite whilst on the other hand Ca, Mg, Mn, Na, K, Ti were reported to be depleted.. Silica was relatively stable from basement to the topsoil in the profile. The CIA generally ranged between 80 - 99The lateritic profiles over banded gneiss, granite and porphyritic granite of Idi-Ayunre and Akure areas varied with the composition of the parent rocks. The thick clayey layers could be of great economic importance for the production of ceramics wares and for constructional purposes.
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Scott, D. J., N. Machado, S. Hanmer, and C. Gariépy. "Dating ductile deformation using U–Pb geochronology: examples from the Gilbert River Belt, Grenville Province, Labrador, Canada." Canadian Journal of Earth Sciences 30, no. 7 (July 1, 1993): 1458–69. http://dx.doi.org/10.1139/e93-126.
Повний текст джерелаАнотація:
The Gilbert River Belt, in the Grenville Province in southeastern Labrador, is a distinctive, west–northwest-trending zone of locally intense deformation and voluminous granitoid plutonism, up to 30 km in width. In an attempt to directly quantify the timing of deformation in ductile shear zones within the belt, rocks interpreted as having been intruded synchronously with ongoing deformation were sampled for U–Pb isotopic analysis. Three of these samples are <2 m wide granitic veins that have sharp intrusive contacts that truncate ductile deformation fabrics, but are themselves deformed at metamorphic conditions similar to their host rocks and are therefore interpreted as having intruded after the initiation of deformation and fabric development, but prior to cessation of this deformation. The first vein is syntectonic with respect to amphibolite-facies deformation and yielded a zircon age of [Formula: see text]. The second vein intruded synchronously with the development of a zone of amphibolite-facies straight gneisses, which defines the southern limit of the Gilbert River belt at [Formula: see text]. The third vein is syntectonic with respect to greenschist-facies deformation and yielded a zircon age of [Formula: see text] and a monazite age of 1078 ± 2 Ma. A sample of the K-feldspar megacrystic granite that underlies much of the belt and is interpreted as having intruded during ongoing amphibolite-facies deformation yielded a zircon age of [Formula: see text]; a mildly deformed granitic vein that crosscuts the megacrystic granite at the same location contained zircon that indicate a [Formula: see text] crystallization age. Monazite from a granodioritic gneiss yielded a concordant age of 1077 ± 3 Ma, interpreted as the time of final cooling during gneiss formation. These results indicate that much of the amphibolite-facies deformation (1664 – 1644 Ma) in the Gilbert River Belt is correlative with the regionally extensive Labradorian orogenic event, whereas greenschist-facies deformation (1113 – 1062 Ma) and monazite growth (1078 Ma) are the result of renewed tectonomagmatic activity during Grenvillian orogenesis.
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Chen, Xu, Chunhua Wen, Debao Meng, Bin Li, Biguang Jiang, and Jinning Qin. "Implications of Major and Trace Element Migration in Altered Granites for Hydrothermal Alteration and Granite-Related Uranium Mineralization in the Sanjiu Ore Field, South China." Minerals 12, no. 2 (January 25, 2022): 144. http://dx.doi.org/10.3390/min12020144.
Повний текст джерелаАнотація:
The recently discovered Sanjiu ore field (SJOF) is a granite-related uranium ore field located in the middle of Zhuguangshan (South China). The relationship between hydrothermal alteration of granite and uranium mineralization in the SJOF is crucial yet understudied. In this study, the major- and trace-element contents of granite samples (fresh granite, altered granite, and tectonites) with different uranium contents were analyzed by using X-ray fluorescence spectroscopy (XRF) and inductively coupled plasma–mass spectrometry (ICP–MS). The analytical results show a relative increase in Si, S, Ca, Pb, Mo, and Sb content in altered granites and tectonites, relative to fresh granites. During the mineralization stage, the increase of the aforementioned elements is related to various hydrothermal alterations (e.g., silicification, carbonation, sulfation, etc.) and newly formed minerals (e.g., microfine crystalline quartz veins; calcite agglomerates or fine veins; and metal sulfides, such as pyrite). There is a concomitant relative decrease in Na, K, Al, Fe, Mg, and other elemental contents that may be due to mineralogical alteration processes, such as biotite to chlorite, feldspar-group minerals to clay minerals, and redox of Fe-bearing minerals. The LREE/HREE ratio in altered granites decreases significantly with the increase in uranium content, suggesting that a low LREE/HREE ratio may be a prospecting indicator. The normalized trace-element patterns of mineralized granite (ore) and the relatively high U content of fresh granite imply that granitic rocks may be the primary uranium source in the SJOF. The uranium mineralization is mainly concentrated in the redox zone that occurs at a depth of 100−300 m. The redox zone is characterized by the most developed hydrothermal alterations and enrichment of trace elements, including W, Mo, Sb, Li, and the HREE.
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Brugger, J., J. Ogierman, A. Pring, H. Waldron, and U. Kolitsch. "Origin of the secondary REE-minerals at the Paratoo copper deposit near Yunta, South Australia." Mineralogical Magazine 70, no. 6 (December 2006): 609–27. http://dx.doi.org/10.1180/0026461067060361.
Повний текст джерелаАнотація:
AbstractThe Paratoo copper deposit, located in the Neoproterozoic to Cambrian Adelaide Geosyncline, South Australia, produced around 360 tons of Cu between 1888 and 1967 from oxidized ores. The deposit is located in the core of a breached, doubly plunging anticline, near a zone of disruption containing brecciated Adelaidean sedimentary rocks and dolerite (‘Paratoo Diapir’), and hosted in dolomitic shales of the Neoproterozoic Burra Formation. Near the surface, the mineralization resides mainly in deeply weathered quartz-magnetite-sulphide (pyrite, chalcopyrite) veins (⩽10 cm wide). At depth, drill cores reveal disseminated magnetite, pyrite, chalcopyrite, copper sulphide and native copper associated with extensive potassic alteration. K-Na-rich fluids also affected the dolerite in the ‘Paratoo diapir’, resulting in the precipitation of K-feldspar, dravite and K-bearing chabazite-Na. The most likely scenario for the genesis of the Paratoo deposit involves circulation of basinal fluids, focusing into the ‘Paratoo Diapir’, and ore precipitation through neutralization by fluid-rock interaction with the dolomitic shales hosting the mineralization.The Paratoo deposit is deeply weathered, with malachite and chrysocolla (± tenorite and cuprite) containing the bulk of the copper recovered from the shallow workings. A diverse assemblage of secondary REE-bearing carbonate minerals, including the new species decrespignyite-(Y) and paratooite-(La), is associated with the weathered base metal and magnetite ores. Whole-rock geochemical analyses of fresh and mineralized host rock and of vein material reveals that the mineralization is associated with a strong, albeit highly variable, enrichment in light rare earth elements (LREE). This association indicates that REE and base metals were introduced by the same hydrothermal fluid. The strong negative Ce anomaly found in secondary REE minerals and mineralized rock samples suggests an upgrade of the REE contents in the weathering zone, insoluble Ce4+ being left behind.The Fe-oxide-REE-base metal association at Paratoo is also characteristic of the giant Mesoproterozoic Fe oxide copper gold deposit of Olympic Dam, located 350 km to the NW. A similar association is found in the Palaeozoic deposits of the Mt Painter Inlier, 300 km to the NNE. The widespread occurrence of this elemental association in the Province probably reflects the geochemistry of the basement, which contains numerous Mesoproterozoic granites enriched in REE and U.
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Landry, Kerstin, Erin Adlakha, Andree Roy-Garand, Anna Terekhova, Jacob Hanley, Hendrik Falck, and Edith Martel. "Uranium Mineralization in the MacInnis Lake Area, Nonacho Basin, Northwest Territories: Potential Linkages to Metasomatic Iron Alkali-Calcic Systems." Minerals 12, no. 12 (December 14, 2022): 1609. http://dx.doi.org/10.3390/min12121609.
Повний текст джерелаАнотація:
The intracratonic Paleoproterozoic Nonacho Basin, deposited on the western margin of the Rae craton, contains historic polymetallic (i.e., U, Cu, Fe, Pb, Zn, Ag) occurrences spatially associated with its unconformable contact with underlying crystalline basement rocks and regionally occurring faults. This study presents the paragenesis, mineral chemistry and geochemistry of uranium mineralized rocks and minerals of the MacInnis Lake sub-basin of the Nonacho Basin, to evaluate the style and relative timing of uranium mineralization. Mineralization is restricted to regionally occurring deformation zones, and post-dates widely spread and pervasive albitization and more local Ba-rich K-feldspar alteration of host rocks. Uranium mineralized rocks show elevated concentration of Cu, Ag and Au relative to variably altered host rocks. Microscopic and compositionally heterogeneous altered uraninite occurs (i) as overgrowths on partially dissolved Cu-sulphides with magnetite in chlorite ± quartz, calcite veins, and (ii) with minor uranophane in hematite-sericite-chlorite ± quartz breccia and stockwork. Both uraninite types are Th poor (<0.09 wt.% ThO2) and variably rich in SO4 (up to 2.26 wt.%), suggesting a low-temperature hydrothermal origin in a relatively oxidized environment. Rare-earth element (+Y) concentrations in type-i uraninite are high, up to 9.5 wt.% Σ(REE+Y)2O3 with CeN/YN values > 1, similar to REE compositions of uraninite in metasomatic iron and alkali-calcic systems (MIAC), including low-temperature hematite-type IOCG-deposits (e.g., Olympic Dam, Gawler Craton, Australia) and albitite-hosted uranium deposits (e.g., Southern Breccia, Great Bear Magmatic Zone, Canada, and Gunnar Deposit, Beaverlodge District, Canada). Both uraninite types are variably rich in Ba (up to 3 wt.% BaO), a geochemical marker for MIAC systems, provided by the dissolution of earlier secondary Ba-rich K-feldspar. Chemical U-Th-Pb dating yields minimum ages of 1757 to 1739 ± 70 Ma for type-ii uraninite-uranophane, consistent with strike-slip movement along regional structures of the basin. We suggest that MacInnis Lake uranium occurrences formed from oxidized hydrothermal fluids along previously altered (albitized, potassically altered) regional-scale faults. Uranium minerals precipitated on earlier Fe-rich sulfides (chalcopyrite, bornite), which acted as a redox trap for mineralization, in low-temperature (~310–330 °C, based on Al-in-chlorite thermometry) breccias and stockwork zones, late in a metasomatic iron and alkali-calcic alteration system.
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Wang, Shuo, Zhanjin Liu, Yunhua Liu, Nan Deng, Benzhao Yang, and Le Tan. "Contribution of Triassic Tectonomagmatic Activity to the Mineralization of Liziyuan Orogenic Gold Deposits, West Qinling Orogenic Belt, China." Minerals 13, no. 1 (January 16, 2023): 130. http://dx.doi.org/10.3390/min13010130.
Повний текст джерелаАнотація:
The Western Qinling orogenic belt (WQOB) is one of the most important prospective gold districts in China, with widely distributed Indosinian intermediate–acidic intrusions. The Liziyuan Au deposit is a representative orogenic deposit in the northern WQOB, hosting several sections spatially associated with igneous rocks. The Au deposit is hosted by meta-sedimentary volcanic rocks of the Cambrian–Ordovician Liziyuan Group and the Tianzishan monzogranite. Two periods, including five stages of mineralization, are recognized in this area: an early metamorphic mineralization period (PI), including quartz–pyrite (Stage I) and banded quartz–polymetallic sulfide (Stage II) veins, and a later magmatic mineralization period (PII) including quartz–K-feldspar–pyrite–molybdenite veins (Stage III), quartz–polymetallic sulfide–chlorite ± calcite veinlets and stockwork (Stage IV), and late calcite–quartz veinlets (Stage V). Geochronological studies indicate a SHRIMP zircon U-Pb age of 236.1 Ma for the Tianzishan monzogranite, and our published ages of ore-bearing diorite porphyrite of the Suishizi section and granite porphyry of the Jiancaowan section being 213 and 212 Ma, respectively. Pyrites formed in association with PI and PII mineralization have well-defined Rb–Sr ages of 220 ± 7.5, 205.8 ± 8.7, and 199 ± 15 Ma, with close temporospatial coupling between mineralization and magmatism. The δ18O and δD values of fluid inclusions in Stage IV auriferous quartz veins range from −0.03‰ to +5.24‰ and −93‰ to −75‰, respectively, suggesting that mineralizing fluid was likely of magmatic origin. Three distinct ranges of δ34S values are identified in the studied sections (i.e., 7.04‰–9.12‰, −4.95‰ to −2.44‰, and 0.10‰–3.08‰), indicating a source containing multiple sulfur isotopes derived from magmatic and metamorphic fluids. The Liziyuan Au deposit is thus likely an orogenic deposit closely related to magmatism. Geochemical characteristics indicate that Tianzishan monzogranite is adakitic and was derived from thickened lower crust during Triassic orogenesis. The ore-bearing diorite porphyrite and granite porphyry formed in a post-collision extensional setting. Together with previous geological and geochemical data, our results indicate that the Liziyuan orogenic Au deposit was formed by early collisional–compressional metamorphism and late post-collision extensional magmatic fluids related to the evolution of the WQOB.
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Melfos, Vasilios, Panagiotis Voudouris, Margarita Melfou, Matías G. Sánchez, Lambrini Papadopoulou, Anestis Filippidis, Paul G. Spry, et al. "Mineralogical Constraints on the Potassic and Sodic-Calcic Hydrothermal Alteration and Vein-Type Mineralization of the Maronia Porphyry Cu-Mo ± Re ± Au Deposit in NE Greece." Minerals 10, no. 2 (February 18, 2020): 182. http://dx.doi.org/10.3390/min10020182.
Повний текст джерелаАнотація:
The Maronia Cu-Mo ± Re ± Au deposit is spatially related to a microgranite porphyry that intruded an Oligocene monzonite along the Mesozoic Circum-Rhodope belt in Thrace, NE Greece. The magmatic rocks and associated metallic mineralization show plastic and cataclastic features at the south-eastern margin of the deposit that implies emplacement at the ductile-brittle transition, adjacent to a shear zone at the footwall of the Maronia detachment fault. The conversion from ductile to brittle deformation caused a rapid upward magmatic fluid flow and increased the volume of water that interacted with the host rocks through high permeable zones, which produced extensive zones of potassic and sodic-calcic alteration. Potassic alteration is characterized by secondary biotite + K-feldspar (orthoclase) + magnetite + rutile + quartz ± apatite and commonly contains sulfides (pyrite, chalcopyrite, pyrrhotite). Sodic-calcic alteration consists of actinolite + sodic-calcic plagioclase (albite/oligoclase/andesine) + titanite + magnetite + chlorite + quartz ± calcite ± epidote-allanite. The high-oxidation state of the magmas and the hydrothermal fluid circulation were responsible for the metal and sulfur enrichments of the aqueous fluid phase, an increase in O2 gas content, the breakdown of the magmatic silicates and the production of the extensive potassic and sodic-calcic alterations. Brittle deformation also promoted the rapid upward fluid flow and caused interactions with the surrounding host rocks along the high temperature M-, EB-, A- and B-type veins.
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Assadi, Aziza O., Nomo N. Emmanuel, and Yamgouot N. Fadimatou. "Petrogenesis and Tectonic Setting of the Gold-Bearing Magmatic Rocks of the North-Western Melfi Massif, Central Chad." European Journal of Environment and Earth Sciences 3, no. 4 (July 13, 2022): 23–31. http://dx.doi.org/10.24018/ejgeo.2022.3.4.304.
Повний текст джерелаАнотація:
This paper presents petrographic and geochemical data on magmatic rocks of the north-western Melfi massif (part of the Gera Massif at the center of Chad) in the Adamawa-Yadé domain. The study area consists of syenite and granite, all crosscut by minor dykes and quartz veins. Syenite and granite show porphyritic texture and are dominated by K-feldspar and plagioclase phenocrysts, biotite, a variable proportion of quartz, and often few amphiboles. These rocks are characterized by low Mg#, Ni and Co, high K2O, Na2O, LREE/HREE ratio, I-type geochemistry as well as positive Eu anomaly, suggesting an origin from partial melting of crustal rocks (here garnet-amphibolite) and metasomatized mantle-derived component with the input of sediments. The compositional evolution from syenites to granite raises the fractional crystallization process in their petrogenesis and involves the fractionation of amphibole, biotite, plagioclase, apatite, magnetite, and ilmenite. Studied samples are affected by the post-magmatic hydrothermal alteration with an assemblage made of epidote, biotite, sericite, and opaques minerals. In addition, they are characterized by considerable gold concentration (Au = 0.6-3.8 ppm) suggesting that the north-western part of the Melfi massif in the center of Chad is a preferential site of gold mineralization. The K-rich calc-alkaline to shoshonitic geochemistry and the pronounced Nb, Ta, and Ti negative anomalies of these rocks, combined with their high Nb/Ta (7.55-32.10), La/Nb (1.80-11.73), and La/Ta (21.53-376.60) ratios but low Rb (57.60-138.30 ppm) indicate that they are subduction-related or arc-related magmas belonging to the Great Central Gondwana Arc (GCGA) formed further to east-directed subduction direction.