Статті в журналах: "Albite alteration"

1

Ernowo, Ernowo, Arifudin Idrus, and Franz Michael Meyer. "Elemental Gains and Losses during Hydrothermal Alteration in Awak Mas Gold Deposit, Sulawesi Island, Indonesia: Constraints from Balanced Mineral Reactions." Minerals 12, no. 12 (December 17, 2022): 1630. http://dx.doi.org/10.3390/min12121630.

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Hydrothermal gold mineralization is commonly associated with metasomatic processes resulting from interaction of hostrock with infiltrating hot aqueous fluids. Understanding of the alteration mechanism requires quantification of element changes in altered rock, relative to the unaltered or least-altered rock, representing the protolith. Balanced mineral reactions are used to gain quantitative insight into the alteration process associated with gold mineralization at the Awak Mas deposit. Three representative samples were carefully selected from the least-altered pyllite and the two alteration zones bordering the mineralization. Mineral mode, textural features, and mineral compositions were studied by microscopy and electron microprobe analyzer (EMPA). Quantitative modal analysis was performed with a Quanta 650 F QEMSCAN® system. The hydrothermal alteration sequence around the mineralization starts with the proximal albite–ankerite–pyrite alteration zone via the distal albite–chlorite alteration zone to the least-altered phyllite wall-rock. Balanced mineral reaction calculations were performed to evaluate elemental gains and losses. Most noticeable is the addition of Si, Na and Ca to each alteration zone. This alteration is represented by the almost complete replacement of muscovite by albite. The addition of Fe and S was highest in the albite–ankerite–pyrite alteration zone. Alteration of the least altered phyllite to the albite–chlorite zone involved a mass increase of 14.5% and a neglectable volume increase of 0.6%. The mass and a volume increase from the least altered phyllite to the albite–ankerite–pyrite zone was 40.5% and 0.47%, respectively. The very low volume change during alteration is also corroborated by the textural preservation indicating isovolumetric metasomatic reactions. The replacement of muscovite by albite may have had an important effect on the change of the rock failure mode from ductile to brittle, with consequences for the focusing of fluid flow.

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Lee, Martin R., Kim A. Waldron, and Ian Parsons. "Exsolution and alteration microtextures in alkali feldspar phenocrysts from the Shap granite." Mineralogical Magazine 59, no. 394 (March 1995): 63–78. http://dx.doi.org/10.1180/minmag.1995.59.394.06.

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AbstractAlkali feldspar phenocrysts (bulk composition Or75.0Ab24.6An0.4) in the subsolvus Shap granite comprise a fine-scale mixture of subregular pristine crypto- and micro-perthites with altered, micropore-rich feldspar with irregular microstructures. The regular perthites are strain-controlled intergrowths of Albite and/or Periclinetwinned albite exsolution lamellae within tweed orthoclase. The microperthites formed at ⩽ 590°C by heterogeneous nucleation of thin albite films which coarsened to > 1 µm length. Cryptoperthites developed at < 400°C by homogeneous nucleation of sub-µm long platelets between films. Platelets are coherent, but the coarser microperthite lamellae are semi-coherent, with pairs of misfit dislocations sub-regularly spaced along the albite-orthoclase interface. As much as 30% of any one feldspar crystal is turbid, a result of the formation of numerous µm to sub-µm sized micropores during deuteric alteration. In some areas, deuteric fluids gained access to the interior of feldspar crystals by exploiting semi-coherent film lamellae. Albite was selectively dissolved and micropore-rich irregular microcline was reprecipitated in its place. In other parts of the feldspars deuteric recrystallization completely cross-cuts the pristine microtextures and patch perthites have formed. These are coarse, incoherent to semi-coherent intergrowths of irregular microcline (replacing tweed orthoclase) and Albite-twinned albite. The deuteric reactions occurred at < 400°C; the main driving force for dissolution and reprecipitation was decrease in the elastic strain energy at the coherent interfaces of crypto-and micro-perthite lamellae, and the recrystallization of tweed orthoclase to irregular microcline.

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Almeida, Delia Del Pilar M. de, Vitor P. Pereira, Adriane Machado, Henrique Zerfass, and Ricardo Freitas. "Late sodic metasomatism evidences in bimodal volcanic rocks of the Acampamento Velho Alloformation, Neoproterozoic III, southern Brazil." Anais da Academia Brasileira de Ciências 79, no. 4 (December 2007): 725–37. http://dx.doi.org/10.1590/s0001-37652007000400012.

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A mineralogical study was carried out in mafic and felsic volcanic rocks of the Acampamento Velho Alloformation at Cerro do Bugio, Perau and Serra de Santa Bárbara areas (Camaquã Basin) in southern Brazil. The Acampamento Velho bimodal event consists of two associations: lower mafic at the base and upper felsic at the top. Plagioclase and alkali-feldspar were studied using an electronic microprobe, and magnetite, ilmenite, rutile, illite and alkali-feldspar were investigated through scanning electron microscopy. The rocks were affected by a process of late sodic autometasomatism. In mafic rocks, Ca-plagioclase was transformed to albite and pyroxenes were altered. In felsic rocks, sanidine was partially pseudomorphosed, generating heterogeneous alkali-feldspar. In this association, unstable Ti-rich magnetite was replaced by rutile and ilmenite. In mafic rocks, the crystallization sequence was: (1) Ti-rich magnetite (?), (2) pyroxene and Ca-plagioclase, (3) albite (alteration to Ca-plagioclase), (4) sericite, chlorite and calcite (alteration to pyroxene), and kaolinite (alteration to plagioclase/albite). In felsic rocks: (1) zircon, (2) Ti-rich magnetite, (3) sanidine, (4) quartz. The introduction of late Na-rich fluids, generated the formation of (5) heterogeneous alkali-feldspar, (6) ilmenite and rutile from the Ti-rich magnetite, (7) albite in the spherulites. Finally, alteration of sanidine, vitroclasts and pumice to (8) illite.

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4

Kawano, Motoharu. "Growth of Smectite from Leached Layer During Experimental Alteration of Albite." Clays and Clay Minerals 42, no. 1 (1994): 7–17. http://dx.doi.org/10.1346/ccmn.1994.0420102.

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Μάραντος, Ι., Γ. Κοσιάρης, Σ. Καραντάση, Β. Περδικάτσης та Γ. Χρηστίδης. "PRELIMINARY STUDY OF ALTERED TERTIARY VOLCANICLASTIC ROCKS IN THE AREA OF ASPROULA , ΝΕΑ SANTA, RODOPI PERFECTURE, THRACE, NE GREECE". Bulletin of the Geological Society of Greece 36, № 1 (1 січня 2004): 454. http://dx.doi.org/10.12681/bgsg.16736.

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The area of Asproula is part of the Tertiary volcanosedimentary basin of Komotini, West Thrace. The geological structure of the area comprises metamorphic rocks of the Rhodope zone and Tertiary volcano-sedimentary rocks. The Tertiary sequence consists of three units: a) the lower unit, in contact with metamorphic rocks comprises sandstones-siltstones b) a unit, which comprises andesitic tuffs and c) a highe: unit consisting of dacitic-rhyodacitic volcaniclastics alternated with tuffites, siltstones, sandstones and marls forming a sequence about 150m thick. The acid volcaniclastics have been altered to clay minerals (mixed layer l-S, kaolinite, ), analcime, albite, and mordenite. The andesitic tuffs are slightly altered to smectite. Moreover in the andesitic tuffs laumontite and scolecite have formed along faults . According to the distribution of characteristic alteration minerals a zonation of alteration has been distinguished. Hence, the lower part of dacitic- ryodacitic tuffs has been altered to analcime + mixed layer l-S + quartz or albite + l-S + quartz, whereas in the upper part the volcaniclastics have been altered to kaolinite or mordenite. In the upper part of the dacitic-rhyodacitic sequence mordenite occurs in distinct thin pyroclastic flows (<5m thickness). The mode of succession of the mordenitic-kaolinitic alteration in the upper parts of the volcaniclastic sequence suggests rapid change in the chemistry of the mineral forming fluids. It is possible that temperature controlled the formation of mordenite. The presence of R1 ordered mixed layer l-S throughout the stratigraphie sequence suggests that the temperature during alteration exceeded 90° C. Moreover, the appearance of neo-formed albite in the lower part of the succession suggests that the temperature during alteration exceeded 120° C, in the lower parts of the formation.

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Kempe, U., J. Götze, S. Dandar, and D. Habermann. "Magmatic and metasomatic processes during formation of the Nb-Zr-REE deposits Khaldzan Buregte and Tsakhir (Mongolian Altai): Indications from a combined CL-SEM Study." Mineralogical Magazine 63, no. 2 (April 1999): 165–77. http://dx.doi.org/10.1180/002646199548402.

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AbstractCathodoluminescence (CL) imaging and spectroscopy, as well as backscattered electron imaging, were used to assign the occurrence of several mineral phases and rock structures in altered nordmarkites and calcite-bearing granites from the Nb-Zr-REE deposits from Khaldzan Buregte and Tsakhir (Mongolian Altai) to three events: (1) intrusion of barren nordmarkites; (2) intrusion of small bodies of calcite-bearing granites with metasomatic alteration of the wall-rocks; and (3) alteration by F-rich fluids.Unusual red and yellow CL caused by Fe3+ and Mn2+ emission centres were detected in microcline and albite. Fe3+ centres were also established (along with others) in quartz, zircon, and possibly in fluorite.Magmatic and metasomatic rock structures and internal structures of the minerals coexist in the samples. The primary magmatic features were in part preserved during alteration. In contrast, the internal and the centre structures may be changed during alteration even in non-replaced mineral phases. Euhedral minerals may be formed by secondary processes as shown for lath-shaped albite. The occurrence of pseudomorphs, the inheritance of elements during replacement, and the mechanical effects of secondary minerals on earlier mineral phases during metasomatic growth are proposed as criteria for the reconstruction of the mineral succession in altered rocks. Snowball structures may be formed as a result of metasomatic alteration rather than as a magmatic intergrowth.

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Calder, Michael F., Zhaoshan Chang, Antonio Arribas, Alina Gaibor, Peter Dunkley, Jeffrey Pastoral, Kalin Kouzmanov, Carl Spandler, and Jeffrey W. Hedenquist. "High-Grade Copper and Gold Deposited During Postpotassic Chlorite-White Mica-Albite Stage in the Far Southeast Porphyry Deposit, Philippines." Economic Geology 117, no. 7 (November 1, 2022): 1573–96. http://dx.doi.org/10.5382/econgeo.4940.

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Abstract Ninety-eight underground diamond holes (~102 km) drilled by Far Southeast Gold Resources Inc. at the Far Southeast porphyry Cu-Au deposit, Philippines, from 2011 to mid-2013, provide a three-dimensional exposure of the deposit between 700- and –750-m elevation, with surface at ~1,400-m elevation. Far Southeast contains an inferred resource of 891.7 million tonnes (Mt) averaging 0.7 g/t Au and 0.5 wt % Cu, equivalent to 19.8 Moz Au and 4.5 Mt Cu. This contribution reports the spatial and temporal distribution of alteration and mineralization at Far Southeast, notably a white-mica–chlorite-albite assemblage that formed after early secondary biotite and before late quartz–white-mica–pyrite alteration and that is associated with the highest copper and gold grades. Alteration assemblages were determined by drill core logging, short-wavelength infrared (SWIR) spectral analysis, petrographic examination, and a quantitative evaluation of materials by scanning electron microscopy (QEMSCAN) study. Alteration is limited around sparse veins or pervasive where vein density is high and the alteration halos coalesce. The alteration and mineralization zones with increasing depth are as follows: (1) the lithocap of quartz-alunite–dominated advanced argillic-silicic alteration that hosts part of the Lepanto high-sulfidation Cu-Au epithermal deposit (mostly above ~700-m elevation), (2) an aluminosilicate-dominated zone with coexisting pyrophyllite-diaspore ± kandite ± alunite and white mica (~700- to ~100-m elevation), (3) porphyry-style assemblages characterized by stockwork veins (below ~500-m elevation), (4) the 1 wt % Cu equivalent ore shell (~400- to –300-m elevation), and (5) an underlying subeconomic zone (about –300- to –750-m elevation, the base of drilling). The ore shells have a typical bell shape centered on a dioritic intrusive complex. The paragenetic sequence of the porphyry deposit includes stage 1 granular gray to white quartz-rich (± anhydrite ± magnetite ± biotite) veins with biotite-magnetite alteration. These were cut by stage 2 lavender-colored euhedral quartz-rich (± anhydrite ± sulfides) veins, with halos of greenish white-mica–chlorite-albite alteration. The white mica is largely illite, with an average 2,203-nm Al-OH wavelength position. The albite may reflect the mafic nature of the diorite magmatism. The quartz veins of this stage are associated with the bulk of copper deposited as chalcopyrite and bornite, as well as gold. Thin Cu sulfide (chalcopyrite, minor bornite) veins with minor quartz and/or anhydrite (paint veins), with or without a white-mica halo, also occur. These veins were followed by stage 3 anhydrite-rich pyrite-quartz veins with white-mica (avg 2,197 nm, illite)–pyrite alteration halos. Combined with previous studies, we conclude that this porphyry system, including the Far Southeast porphyry and Lepanto high-sulfidation Cu-Au deposits, evolved over a period of 0.1–0.2 m.y. Three diorite porphyry stocks were emplaced, and by ~1.4 Ma biotite-magnetite–style alteration formed with quartz-anhydrite veins and deposition of ≤0.5% Cu and ≤0.5 g/t Au (stage 1); coupled with this alteration style, a barren lithocap of residual quartz with quartz-alunite halo plus kandite ± pyrophyllite and/or diaspore formed at shallower depth (>700-m elevation). Subsequently, lavender quartz and anhydrite veins with bornite and chalcopyrite (high-grade stage, avg ~1 wt % Cu and ~1 g/t Au) and white-mica–chlorite-albite halos formed below ~400-m elevation (stage 2). They were accompanied by local pyrite replacement, the formation of hydrothermal breccias and Cu sulfide (paint) veins. Stage 2 was followed at ~1.3 Ma by the formation of igneous breccias largely along the margins of the high-grade zones and stage 3 pyrite-quartz-anhydrite ± chalcopyrite veins with white-mica (mostly illitic) halos. At shallower depths in the transition to the base of the lithocap, cooling led to the formation of aluminosilicate minerals (mainly pyrophyllite ± diaspore ± dickite) with anhydrite plus high-sulfidation-state sulfides and pyrite veinlets. Consistent with previous studies, it is likely that the lithocap-hosted enargite-Au mineralization formed during this later period.

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Bérubé, Charles L., Gema R. Olivo, Michel Chouteau, and Stéphane Perrouty. "Mineralogical and textural controls on spectral induced polarization signatures of the Canadian Malartic gold deposit: Applications to mineral exploration." GEOPHYSICS 84, no. 2 (March 1, 2019): B135—B151. http://dx.doi.org/10.1190/geo2018-0404.1.

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Applications of the spectral induced polarization (SIP) method to mineral exploration are limited by our knowledge of the relationships among rock texture, mineral composition, and electrical properties. Laboratory SIP responses were measured on rock samples from the Canadian Malartic gold deposit. Field SIP responses were also measured at the outcrop scale, along a profile that intersects a well-studied mineralized zone. The mineralogy and the texture of sedimentary rocks from this deposit were quantitatively determined with mineral liberation analysis. A systematic decrease (Pearson [Formula: see text]) in total chargeability with increasing fraction of the sulfide mineral interfaces associated with feldspar minerals (namely, K-feldspar and albite) was observed. On the other hand, total chargeability increased with the fraction of sulfide mineral interfaces associated with carbonates and micas (Pearson [Formula: see text]). At Canadian Malartic, proximal alteration in the mineralized zones is marked by rocks that lack a foliation plane and that were subjected to pervasive K-feldspar, albite, and pyrite alteration. In contrast, distal alteration in sedimentary rocks is marked by biotite, albite, carbonate, and pyrite that are oriented along the regional [Formula: see text] foliation. In the least-altered (LA) sedimentary rocks, quartz and biotite are associated with pyrrhotite and ilmenite as the main sulfide and oxide mineral phases, respectively. SIP measurements conducted at district and outcrop scales and along a drill core indicated that proximally altered sedimentary rocks were characterized by low total chargeability values ([Formula: see text] to [Formula: see text] in the laboratory and [Formula: see text] in the field). In contrast, the LA sedimentary rocks were characterized by total chargeability values up to [Formula: see text] in the laboratory and [Formula: see text] in the field. We conclude that mineralized zones associated with this type of ore deposit are characterized by low chargeability anomalies.

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Bevins, R. E. "Pumpellyite-dominated metadomain alteration at Builth Wells, Wales–evidence for a fossil submarine hydrothermal system?" Mineralogical Magazine 49, no. 352 (June 1985): 451–56. http://dx.doi.org/10.1180/minmag.1985.049.352.15.

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AbstractTwo metamorphic alteration styles have been observed in basic lavas and volcaniclastic rocks of the Builth Volcanic Series of Ordovician age exposed at Llanelwedd Quarry, in the Builth lnlier, Wales. The first alteration style is characterized by the development of a mineral assemblage comprising albite+chlorite+ sphene+ pumpellyite ± prehnite ± calcite ± white mica, although original textures are largely preserved. This alteration pattern corresponds with that developed in volcanic and volcaniclastic rocks elsewhere in Wales, and which is attributed to the effects of burial. The second alteration style is characterized by the development of metadomains dominated by pumpellyite or, more rarely, prehnite. In the metadomains no original textures are seen in hand specimen. This alteration pattern has, so far, not been observed elsewhere in Wales, and it is here suggested that it might result from a submarine hydrothermal circulation system.

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Sarmili, Lili, and Johanes Hutabarat. "INDICATION OF HYDROTHERMAL ALTERATION ACTIVITIES BASED ON PETROGRAPHY OF VOLCANIC ROCKS IN ABANG KOMBA SUBMARINE VOLCANO, EAST FLORES SEA." BULLETIN OF THE MARINE GEOLOGY 29, no. 2 (February 15, 2016): 91. http://dx.doi.org/10.32693/bomg.29.2.2014.69.

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The presence of mineral alteration or secondary processes to rocks on submarine volcano of Abang Komba was caused by an introduction of hydrothermal solutions. Those are indicated by the presence of a resembly of minerals alteration seen in their petrographic analyses. They are characterized by replacement partially surrounding of plagioclase phenocrysts, partially replacing plagioclase by sericite, carbonate and clay minerals. The replacement of pyroxene partly by chlorite, and the presence of albitisation (secondary albite) contained in fine rectangular plagioclase sized. Other fitures occasionally observed by the presence of partial oxidation of ore minerals and the presence of quartz, and epidote as an alteration from plagioclase and pyroxene. Keywords : alteration, resembly of minerals alteration, oxidation, submarine vulcano of Abang Komba. Gejala alterasi atau proses-proses sekunder yang terjadi pada batuan di gunung bawah laut Abang Komba adalah disebabkan oleh introduksi larutan hidrotermal. Semua ini ditunjukkan dengan kehadiran kumpulan mineral ubahan yang terlihat dalam sayatan batuan. Kumpulan mineral ini dicirikan dengan adanya penggantian sebagian yang mengelilingi fenokris plagioklas, penggantian sebagian plagioklas oleh serisit, karbonat dan mineral lempung. Penggantian sebagian piroksen oleh klorit, dan adanya gejala albitisasi (albit sekunder) yang terdapat pada plagioklas berbentuk balokan yang berukuran halus. Gejala lainnya yang kadang-kadang teramati adanya oksidasi sebagian dari mineral bijih dan hadirnya kuarsa, serta epidot sebagai hasil ubahan plagioklas dan piroksen. Kata kunci : alterasi, kumpulan mineral ubahan, oksidasi, gunung bawahlaut Abang Komba.

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11

Mueller, Andreas G., Neal J. McNaughton, and Janet R. Muhling. "Albite ± Actinolite-Altered Porphyry Dykes in Archean Gold Deposits of the Boulder Lefroy-Golden Mile Fault System, Yilgarn Craton, Western Australia: Petrography, Chronology, and Comparison to Canadian Albitites." Minerals 11, no. 11 (November 19, 2021): 1288. http://dx.doi.org/10.3390/min11111288.

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The Boulder Lefroy-Golden Mile fault system in the Archean Yigarn Craton is the most productive gold-mineralized structure in Australia (>2300 t Au). The New Celebration deposit (51 t Au) is part of a group of hematite- and anhydrite-bearing mesothermal deposits and Fe-Cu-Au skarns associated with monzodiorite-tonalite intrusions in the strike-slip fault system. Ore-grade biotite-carbonate and late sericite-carbonate-alkali feldspar replacement is bound to the contacts of a felsic (low Cr, Ni, V) quartz-plagioclase porphyry dyke dated at 2676 ± 7 Ma. The sodic-potassic alteration of the felsic boudinaged dyke contrasts with the albite-actinolite alteration in the adjacent mafic (high Cr, Ni, V) plagioclase porphyry dated at 2662 ± 4 Ma, although both share the same sulfide-oxide assemblage: pyrite ± chalcopyrite, magnetite ± hematite. The younger porphyry locally crosscuts foliation and is bordered by post-kinematic actinolite-pyrite selvages overprinting talc-chlorite-phlogopite-dolomite schist. It contains auriferous pyrite (70 ppb Au; 610 ppb Ag) where sampled for zircon U-Pb chronology at +224 m elevation. Above the sample site, the dyke was mined as gold ore (1–6 g/t Au) at +300–350 m. Temperature estimates based on actinolite-albite pairs (300–350 °C) agree with the fluid inclusion trapping temperature of main-stage auriferous veins (330 ± 20 °C). These relationships are interpreted to indicate syn-mineralization emplacement. Gold-related albite-altered porphyry dykes (albitites) also occur in the world-class Hollinger-McIntyre (986 t Au) and Kerr Addison-Chesterville deposits (336 t Au), Abitibi greenstone belt, Canada.

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Starostin, I. A., M. M. Girfanov, and E. I. Yartsev. "Geological features, hydrothermal alterations, and cryptic mineralogical zonation of the Kyzyk-Chadr porphyry copper deposit (Tyva Republic)." Moscow University Bulletin. Series 4. Geology, no. 5 (December 17, 2022): 90–94. http://dx.doi.org/10.33623/0579-9406-2022-5-78-89.

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The altered rocks of the Kyzyk-Cha dr deposit are predominantly composed of quartz and potassic dioctahedral micas of the phengite–muscovite series, that dominate in almost all zones of the alteration halo. Parageneses of albite with chlorite and epidote are only characteristic of peripheral sections of the halo, subjected to the propylite-type alteration. Quartz-potassium feldspar alterations are distributed in the central and deep-seated sections of the halo. Petrographic investigations of hydrothermal alterations and results of the X-ray structural analysis and infrared (IR) spectroscopy of micas from the mineralized quartz-sericite metasomatites were applied to reveal a cryptic mineralogical zonation of the Kyzyk-Chadr porphyry copper deposit. Elements of the cryptic mineralogical zonation, revealed based on results of the X-ray study and IR spectroscopy of light-colored micaceous metasomatites of the deposit, are caused by variable proportions of the phengite and muscovite components in their composition. The phengite component predominates in the central and deep-seated sections of the alteration-mineralization halo of the deposit, while the muscovite component progressively increases toward its flanks and upper sections. This tendency correlates with the general vector of the mineralogical alteration-mineralization zonation and are supposedly explained by changing PT conditions within the porphyry copper ore-magmatic system. The indicator of the cryptic mineralogical zonation by the “phengite-muscovite” relationship can be applied for prospecting and preliminary evaluation of porphyry copper type deposits, being used as an objective guide for correlation of already obtained ore-grade interceptions and forecasting the ore bodies.

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Møller, S. Karup, J. Rose Hansen, and H. Sørensen. "Eudialyte decomposition minerals with new hitherto undescribed phases from the Ilímaussaq complex, South Greenland." Bulletin of the Geological Society of Denmark 58 (November 10, 2010): 75–88. http://dx.doi.org/10.37570/bgsd-2010-58-06.

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Eudialyte is a distinctive mineral in the agpaitic group of peralkaline nepheline syenites. The paper describes the alteration of eudialyte from the Ilímaussaq complex, South Greenland, which is the type locality for eudialyte, as well as for agpaitic rocks. Two types of alteration are distinguished: alteration of eudialyte to catapleiite is widespread in the complex, whereas alteration to zircon only occurs in strongly altered rocks. additionally, the fol-lowing minerals have been identified in the altered eudialyte: aegirine, K-feldspar, albite, analcime, fluorite, monazite, apatite, allanite, Y-fergusonite, Ce-fergusonite, fersmite, nacareniobsite-(Ce), uranothorianite, neptunite and grossularite. Some unidentified Nb and/or REE minerals have been distinguished. The different styles of alteration can be explained by different late- and post magmatic conditions at different settings in the complex. Alteration to zircon is caused by fluids of external origin or by fluids expelled from intersecting lujavrite and pegmatite dykes. Alteration to catapleiite is caused by late-magmatic interstitial fluids. The alteration has resulted in distinct fractionation of some elements; Zr is, for instance, located only in zircon and catapleiite, Nb and REE in separate minerals.

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Dempster, Tim J., Allan D. Hollinsworth, Euan McIntosh, Shannon Edgar, John W. Faithfull, and Daniel Koehn. "Deformation-Induced and Reaction-Enhanced Permeability in Metabasic Gneisses, Iona, Scotland: Controls and Scales of Retrograde Fluid Movement." Geofluids 2021 (January 27, 2021): 1–18. http://dx.doi.org/10.1155/2021/8811932.

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The spatial distribution of greenschist-facies retrograde reaction products in metabasic gneisses from Iona, western Scotland, has been investigated. The retrograde products may be broadly accounted for by a single reaction, but their different spatial and temporal development indicates that a series of reactions occur with significantly different scales of metasomatic transfer. After initial fluid influx linked to deformation-induced high permeability, reaction-enhanced permeability, coupled to cycling of fluid pressure during faulting, strongly controls the pervasive retrogression. Ca-plagioclase and pyroxene in the gneisses are replaced by albite and chlorite in pseudomorphic textures, and this is followed by localized epidotization of the albite. Two main generations of epidote are formed in the gneisses. Epidosite formation is associated with prominent zones of cataclasite indicating a strong link between faulting and fluid influx. In contrast, complete alteration of albite to epidote in the host metabasic gneisses is spatially complex, and areas of pervasive alteration may be constrained by both epidote-rich veins and cataclasites. In other instances, reaction fronts are unrelated to structural features. Volume changes associated with individual stages of the reaction history strongly control the localized distribution of epidote and the earlier more widespread development of chlorite and albite. Such behaviour contrasts with adjacent granitic gneisses where epidotization is restricted to local structural conduits. Many small-scale mineralized fractures with evidence of having previously contained fluids do not enhance the pervasive retrogression of the metabasic gneisses and represent conduits of fluid removal. Retrogression of these basement gneisses is dominated by a complex combination of reaction-enhanced and reaction-restricted permeability, kinetic controls on the nucleation of reaction products, changes in fluid composition buffered by the reactions, and periodic local migration of fluids associated with fault movements. This combination generates spatially complex patterns of epidotization that are limited by cation supply rather than fluid availability and alternations between focused and pervasive types of retrogression.

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Pal, D. C., and T. Chaudhuri. "Radiation damage-controlled localization of alteration haloes in albite: implications for alteration types and patterns vis-à-vis mineralization and element mobilization." Mineralogy and Petrology 110, no. 6 (July 21, 2016): 823–43. http://dx.doi.org/10.1007/s00710-016-0453-3.

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Marignac, Christian, Michel Cuney, Michel Cathelineau, Andreï Lecomte, Eleonora Carocci, and Filipe Pinto. "The Panasqueira Rare Metal Granite Suites and Their Involvement in the Genesis of the World-Class Panasqueira W–Sn–Cu Vein Deposit: A Petrographic, Mineralogical, and Geochemical Study." Minerals 10, no. 6 (June 23, 2020): 562. http://dx.doi.org/10.3390/min10060562.

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Elucidation of time-space relationships between a given wolframite deposit and the associated granites, the nature of the latter, and their alterations, is a prerequisite to establishing a genetic model. In the case of the world-class Panasqueira deposit, the problem is complicated because the associated granites are concealed and until now poorly known. The study of samples from a recent drill hole and a new gallery allowed a new approach of the Panasqueira granite system. Detailed petrographic, mineralogical, and geochemical studies were conducted, involving bulk major and trace analyses, BSE and CL imaging, EPMA, and SEM-EDS analyses of minerals. The apical part of the Pansqueira pluton consisted of a layered sequence of separate granite pulses, strongly affected by polyphase alteration. The use of pertinent geochemical diagrams (major and trace elements) facilitated the discrimination of magmatic and alteration trends. The studied samples were representative of a magmatic suite of the high-phosphorus peraluminous rare-metal granite type. The less fractionated members were porphyritic protolithionite granites (G1), the more evolved member was an albite-Li-muscovite rare metal granite (G4). Granites showed three types of alteration processes. Early muscovitisation (Ms0) affected the protolithionite in G1. Intense silicification affected the upper G4 cupola. Late muscovitisation (Fe–Li–Ms1) was pervasive in all facies, more intense in the G4 cupola, where quartz replacement yielded quartz-muscovite (pseudo-greisen) and muscovite only (episyenite) rocks. These alterations were prone to yield rare metals to the coeval quartz-wolframite veins.

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17

Sokalska, E. T., E. Dubińska, G. Kaproń, J. A. Kozubowski, and M. Walski. "Clay minerals from Permo-Carboniferous very low-grade metamorphic rocks from the central part of the Fore Sudetic Monocline (western Poland)." Clay Minerals 43, no. 4 (December 2008): 561–74. http://dx.doi.org/10.1180/claymin.2008.043.4.04.

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AbstractThe mafic rocks from boreholes studied here contain the assemblage typical for upper-subgreenschist to lower-greenschist facies (albite, chlorite, illite, titanite, quartz, Ti-oxide ± actinolite) as well as relict clinopyroxene.Metapelites underlying a metabasic rock sequence also record metamorphic alteration as demonstrated by the chlorite and illite crystallinities. Chlorite crystallinity suggests formation in conditions close to the subgreenschist/greenschist facies boundary, but this mineral is partly decomposed during metamorphic retrogression.

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18

Asrafil, Asrafil, Teguh Hilmansyah, Muslimin U. Botjing, and Eka Yuliastri. "Mineralization Study of Volcanic Rocks in Colo Volcano Tojo Una-Una Central Celebes." Jurnal Geomine 8, no. 3 (February 19, 2021): 171. http://dx.doi.org/10.33536/jg.v8i3.705.

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Colo Volcano is an active volcano located on Una-Una Island, Tojo Una-Una Regency, Central Sulawesi Province. Volcanism and magmatism of Mount Colo are still in progress, and this has certainly triggered mineralization in volcanic rocks which is interesting for study. This research aims to reveal the mineralization characteristics of volcanic rocks in the study area. This research was conducted through investigative methods in the form of field observations and laboratory through petrographic and rock chemistry (X-Ray Defraction analysis) to reveal the presence of alteration minerals as a characteristic of mineralization. The results of this study indicate that the volcanic rocks present are tuff and volcanic breccia in the form of pyroclastic deposits associated with alluvial material and andesite rocks. Identification of alteration minerals through XRD test shows the presence of hydrothermal alteration minerals with a formed temperature of 300 ° C such as Quartz, Calcite, Clinochlore, Albite, Dickite, Andesine, and K-Feldspar which are classified into Argillic and Propylitic alteration types.

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19

Yildirim, Demet Kiran. "Genesis of the Halılar Metasediment-Hosted Cu-Pb (±Zn) Mineralization, NW Turkey: Evidence from Mineralogy, Alteration, and Sulfur Isotope Geochemistry." Minerals 12, no. 8 (August 4, 2022): 991. http://dx.doi.org/10.3390/min12080991.

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This study contributes to our understanding of the evolution of Halılar Cu-Pb (±Zn) mineralization (NW Turkey) based on mineralogical and geochemical results and sulfur isotope data. The study area represents local Cu-Pb with some Zn brecciated-stockwork vein type mineralization along the NE–SW fault gouge zone at the lower boundary of the Sakarkaya and Düztarla granitoid rocks. Two main zones, consisting of sericite–quartz–chlorite ± kaolinite ± pyrite (i.e., zone-1) and calcite–epidote–albite ± chlorite ± sericite (i.e., zone-2), were observed within the central ore mineral zone at the mining site. Different mineralization assemblages were recorded; the main ore mineral contains chalcopyrite, galena, pyrite, and sphalerite within alteration zone-1, and the oxidation/supergene mineralization includes covellite and goethite. The mass balance calculations show that the samples of zone-1 show an increase in SiO2, Fe2O3, K2O, and LOI along with Ag, As, Cu, Mo, Pb, S, Sb, and Zn, reflecting high pyritization with sericitization and silicification. On the other hand, the samples from zone-2 are rich in CaO; Na2O; P2O5; TiO2; LOI; and carbon-reflecting calcite, epidote, and albite alterations. A uniform magmatic sulfur source of Halılar sulfides is suggested by their mean δ34S value of −1.62‰. Furthermore, the primary metal source is metasediments and intrusive Düztarla granitoid magmatism. These observations suggest that the Halılar metasediment-hosted Cu-Pb (±Zn) mineralization was formed by epigenetic hydrothermal processes after sedimentation/diagenesis and metamorphism.

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20

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.

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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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21

Alcalde-Aparicio, Sara, M. Vidal-Bardán, and E. Alonso-Herrero. "Mineralogy and geochemical signatures as indicators of differential weathering in natural soil profiles from the West Asturian-Leonese Zone (NW Iberia)." Earth Sciences Research Journal 26, no. 1 (May 11, 2022): 55–66. http://dx.doi.org/10.15446/esrj.v26n1.81087.

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This paper presents detailed mineralogical results together with a geochemical characterization for a sequence of six natural soil profiles. Bedrock samples (R series) and overlying soil samples (S series) were characterized. The soil profiles are distributed in a series of Paleozoic lithological units from lower Ordovician to upper Carboniferous in age (Iberian Massif, NW Iberia). The lithological influence on mineral properties and geochemical composition and, how different weathering may be occurring under very similar temperate and acidic conditions, have been studied. Field observations together with laboratory analyses were indicative of differential weathering. So, a series of selected chemical indices and relations were applied to clarify this assumption. The mineralogy was analysed by Scanning electron microscopy (SEM-EDS), X-ray diffraction (XRD) of rock powder and soil oriented aggregates. X-ray fluorescence spectrometry (XRF) and inductively coupled plasma mass spectroscopy (ICP-MS) were applied to analyse chemical composition. The first results showed how major elements, SiO2, Al2O3 and Fe2O3, slightly enriched in the soil profiles, are consistent with the dominant mineralogy: quartz, chlorite, muscovite and/or illite, together with kaolinite and albite. The bases K2O, Na2O, CaO and MgO are also coherent with mineral composition and experience little variation, but are gradually removed in the profiles. The mobility of major elements leads to a general loss of bases and, in general, a slight enrichment in silica and sesquioxides. SiO2 is enriched, firstly accumulated in soils and partially depleted by dissolution as colloidal form. Al2O3 in some soils is slightly less than in former rocks, so other physical processes are expected to take place, involving clay removal with consequent aluminium depletion too. A special emphasis has been given to albite coexisting with kaolinite, firstly supposed to be directly inherited from parent substrates when present, but finally the chemical index PIA shows it was mainly due to mineral alteration of plagioclases. The best correlations to explain the albite alteration and kaolinitization progress were obtained with chemical indices PIA, CIW, CIA and Al2O3/Na2O ratio. This together with mineralogical signatures, suggest that kaolinite is the result of gradual dissolution due to the acid hydrolysis of albite in such acidic environments, which may also be attributed to the organic matter influence.

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22

Dekayir, A., M. Amouric, and J. Olives. "Clay minerals in hydrothermally altered basalts from Middle Atlas, Morocco." Clay Minerals 40, no. 1 (March 2005): 67–77. http://dx.doi.org/10.1180/0009855054010156.

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AbstractClay minerals occur as replacements of olivine, pyroxenes, plagioclase and interstitial materials, and as vesicle fillings, in altered basalts from the Middle Atlas (Morocco). Phyllosilicates are the main components of this alteration process. They have been characterized here by optical microscopy, X-ray diffraction, scanning electron microscopy and high-resolution transmission electron microscopy as saponite, talc, corrensite and chlorite. The homogeneity of the chemical compositions of these phyllosilicates, in different alteration environments, probably means that they are controlled by the composition of the hydrothermal fluid. Talc-saponite-corrensite (with dominant saponite) is the clay mineral association most frequently observed (corrensite being more abundant in the vesicular levels of the basalts). Such an association, with no evidence of albite and zeolite, suggests that these basalts have suffered minimal alteration at relatively low temperatures. Another association, chlorite-corrensite, was detected in a deeper (vesicular) sample, probably resulting from a slightly higher temperature. Lastly, only discrete phyllosilicates (i.e. no random mixed-layer minerals) were observed. This suggests that near-equilibrium conditions prevailed during this alteration stage and that a dissolution-crystallization process was the main mechanism of transformation.

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23

Ishizuka, H. "Pumpellyite from the oceanic crust, DSDP/ODP Hole 504B." Mineralogical Magazine 63, no. 6 (December 1999): 891–900. http://dx.doi.org/10.1180/minmag.1999.063.6.08.

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AbstractPumpellyite has been found in doleritic basalt of a sheeted dyke complex drilled from 2072.1 m below sea floor in DSDP/ODP Hole 504B, south of the Costa Rica Rift, eastern Pacific. It occurs as fine-grained crystal aggregates accompanied by albite, chlorite and chalcopyrite, which partially replace a plagioclase phenocryst (An85–88) that is also associated with primary magnetite. Chemical compositions of the pumpellyite vary antithetically in relation to Fe* and Al as well as Fe* and Mg, indicating the dominant substitution of Fe3+ by Al with the minor substitution of Fe2+ by Mg. Such compositional variations overlap with those of prehnite-pumpellyite facies rocks dredged from other oceanic ridges and intra-oceanic arcs, and those of similar facies rocks from ophiolites, but are aluminous compared with those of zeolite facies metabasites in ophiolites. These observations suggest that the breakdown of the plagioclase phenocryst and magnetite in the presence of a Cu- and S-bearing fluid phase led to the formation of pumpellyite + albite + chlorite + chalcopyrite during oceanic ridge hydrothermal alteration.

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24

Song, Xiaoxia, Kaijie Li, Hongtao Ma, Dongna Liu, Jingui Zhao, and Jiarui Zhou. "Characteristics of an Altered Diabase Dike in a Coal Seam: A Case Study from the Datong Coalfield, Shanxi, China." Geofluids 2020 (July 7, 2020): 1–14. http://dx.doi.org/10.1155/2020/3593827.

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Carboniferous–Permian coal seams in the Datong coalfield are intruded by Mesozoic magmatic dikes and sills. Our observations indicate that these dikes and sills have been seriously altered and have lost their original characteristics. Although this phenomenon has been mentioned in some studies, there is a lack of detailed research on the alteration mechanism. To fill this research gap, six dike samples were collected in this study to analyze their alteration characteristics and mechanisms. Petrographic analysis, scanning electron microscopy, and X-ray diffraction were used to determine the mineralogy of the altered igneous samples. The results suggest that the mineral alteration is associated with severe carbonation and clavization. The carbonation of mafic minerals is due to the release of CO2 generated from the coking of high volatile bituminous coals that may have occurred during the intrusive event. However, labradorite did not react with CO2. The water activity in the coal seam was enhanced by the dikes, and mafic minerals were converted into mixtures of chlorite and smectite group minerals. The water activity is especially high at the edges of the dike. Albite and clay minerals were formed due to the albitization of labradorite. Based on these effects, the dike can be divided into weak alteration, carbonation, and clavization bands. The alteration processes in the coal seam are described in detail in this work, and potential formation mechanisms are suggested.

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25

Wilde, Andy. "Shear-Hosted Uranium Deposits: A Review." Minerals 10, no. 11 (October 26, 2020): 954. http://dx.doi.org/10.3390/min10110954.

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A group of uranium deposits is described that is hosted within polyphase shear zones. The group is economically significant, collectively containing over 500,000 tonnes of uranium and several examples have been or are being mined. Over a hundred individual deposits are known widely spread over many countries. It is proposed that this group be assigned to a new shear-hosted uranium deposit category. Uranium deposition was superimposed upon intense and extensive feldspathic alteration formed during ductile deformation. This intense alteration has led to the alternative albitite-type or metasomatite-type nomenclature. The evidence is clear that in most cases uranium mineralization postdates regionally extensive feldspar alteration and is associated with a range of alteration assemblages which overprint early albite or K-feldspar dominant alteration. Abundance of hydrothermal zirconium and phosphate minerals is a common characteristic of this group which implies high activity of F and P during mineralisation, but the source of hydrothermal fluids remains uncertain. Also uncertain is the geodynamic setting of uranium mineralisation which is a consequence of absolute mineralisation age being poorly defined. Data from three of the four major districts are suggestive that mineralisation was a consequence of fluid migration along shears during regional compression. This paper reviews key aspects of the group in a mineral systems context, focussing on the four major districts of Kropyvnytskyi (Ukraine), Lagoa Real (Brazil), Mount Isa (Australia) and the Central Mineral Belt (Canada).

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26

Tsuzuki, Yoshiro, and Keiko Ogasawara. "Dissolution experiments on albite and basalt glasses at various temperatures and their application to hydrothermal alteration in geothermal fields." GEOCHEMICAL JOURNAL 21, no. 6 (1987): 261–81. http://dx.doi.org/10.2343/geochemj.21.261.

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27

Grizelj, A., D. Tibljaš, M. Kovačić, and D. Španić. "Diagenesis of Miocene pelitic sedimentary rocks in the Sava Depression (Croatia)." Clay Minerals 46, no. 1 (March 2011): 59–72. http://dx.doi.org/10.1180/claymin.2011.046.1.59.

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AbstractMiocene pelitic sedimentary rocks from six wells in the Sava Depression (sub-basin in the south-western part of the Pannonian Basin System) were investigated in order to determine the degrees of diagenetic alteration.Qualitative and semiquantitative mineral compositions of samples and the content of smectite in illite-smectite (I-S) were determined by X-ray powder diffraction (XRD).Vitrinite reflectance and thermal alteration index (TAI) were measured in order to estimate the palaeotemperatures.Carbonate minerals, clay minerals and quartz are the main constituents of the pelitic sediments.Feldspars (albite), pyrite, opal-CT and hematite are present as minor constituents in some rocks. The mineral composition of the rocks, apart from previously known differences caused by various depositional environments and clastic material provenance, is dependent on the degree of diagenetic processes. At elevated temperatures and large burial depths the minerals formed by alteration processes or precipitated at the surface; smectite, kaolinite and calcite were gradually replaced by minerals formed by diagenetic processes, i.e. by illite-smectite, illite, chlorite, Ca-excess dolomite/ankerite and albite. Based on XRD data for smectite, I-S and illite, three stages of diagenetic development have been established. The early stage was characteristic of samples at depths <1.8 km containing smectite, I-S of the random R0 type and detrital illite.The middle stage begins with the appearance of the ordered R1 type of I-S at the depths >1.8 km and temperature above 80°C. At depths >4.6 km with corresponding temperatures >190ºC, the late stage began, characterized by the presence of R>1 I-S with <10% smectite.

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Kuva, Jukka, Mikko Voutilainen, Antero Lindberg, Joni Parkkonen, Marja Siitari-Kauppi, and Jussi Timonen. "Pore and mineral structure of rock using nano-tomographic imaging." MRS Proceedings 1744 (2015): 235–40. http://dx.doi.org/10.1557/opl.2015.335.

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ABSTRACTIn order to better understand the micrometer-scale structure of rock and its transport properties which arise from it, seven monomineral samples from two sites (Olkiluoto and Sievi, Finland) were studied with micro- and nanotomography and scanning electron microscopy. From the veined gneiss of Olkiluoto we studied biotite, potassium feldspar, plagioclase (composition of oligoclase) and cordierite, and from Sievi tonalite biotite and two grains of plagioclase (albite). These minerals were the main minerals of these samples. Samples were carefully separated and selected using heavy liquid separation and stereomicroscopy, their three dimensional structure was imaged using X-ray tomography, and their precise mineral composition was determined using scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM/EDS). The micrometer-scale mineral structure of these samples was observed together with their pores and fissures, and alteration effects were identified whenever applicable. Nanotomography combined with SEM analysis was concluded to be a good tool for analyzing effects of alteration in monomineral samples.

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Schandl, Eva S., Michael P. Gorton, and Colin J. Bray. "High-temperature brine in chalcopyrite-rich quartz vein 40 km southwest of Sudbury, Ontario." Canadian Journal of Earth Sciences 48, no. 10 (October 2011): 1369–85. http://dx.doi.org/10.1139/e11-033.

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The Lac Panache (Nipissing) gabbro intrudes Huronian metasediments ca. 40 km southwest of the Sudbury Igneous Complex. The gabbro contains disseminated sulfides and is in contact with a chalcopyrite-rich quartz vein that crystallized from highly saline fluids (46.8 ± 3 equivalent wt.% NaCl) at a minimum temperature of 420 ± 27 °C. Chloride and carbonate inclusions in opened fluid inclusion cavities in the vein suggest that the brine contained dissolved metals (in addition to NaCl), such as Fe, Cu, Mn, and Co. The weakly altered quartz vein postdated regional metamorphism and was probably contemporaneous with the 1.7 Ga felsic magmatism and attendant albite alteration in the area. Cl-rich scapolite in the gabbro and highly saline fluid inclusions in the quartz vein suggest the existence of circulating hot brine throughout the tectonic evolution of the region. The 2.2 Ga old gabbro contains an abundance of Cl-rich scapolite intergrown with pyrrhotite and chalcopyrite that formed during the early hydrothermal (deuteric) alteration of the gabbro.

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30

Li, Ruihong, Ntwali Albert, Menghe Yun, Yinsheng Meng, and Hao Du. "Geological and Geochemical Characteristics of the Archean Basement-Hosted Gold Deposit in Pinglidian, Jiaodong Peninsula, Eastern China: Constraints on Auriferous Quartz-Vein Exploration." Minerals 9, no. 1 (January 21, 2019): 62. http://dx.doi.org/10.3390/min9010062.

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The gold deposits that are hosted in the Archean metamorphic rock, have yet to be explored beyond Pinglidian gold deposit in the northwestern Jiaodong Peninsula, eastern China. This kind of gold deposit differs from those that are hosted in Mesozoic granitoids, showing good potential for the prospecting of auriferous quartz-vein gold deposits controlled by the structures in greenfield Archean metamorphic rock. Pinglidian gold deposit is located in the hanging wall of the Jiaojia fault and consists of eight separated orebodies that are enveloped by altered rock in Archean biotite plagiogneiss. These orebodies and wall-rock alterations are strongly controlled by local structures that formed during the Mesozoic rotation and kink folding of the foliated and fissile Archean basement host. The major wall-rock alterations comprise sericitization, silicification, pyritization, and carbonation, which is up to 18 m in width and progressively increases in intensity towards the auriferous quartz vein. The visible gold is present as discrete native gold and electrum grains, which have basically filled in all manner of fractures or are adjacent to galena. We recognize two types of gold bearing quartz veins that are associated with mineral paragenetic sequences during hydrothermal alteration in the Pinglidian gold deposit. The petrological features and geochemical compositions in the reaction fronts of the alteration zone suggest variations in the physicochemical conditions during ore formation. These minerals in the wall rock, such as plagioclase, biotite, zircon, titanite, and magnetite, have been broken down to hydrothermal albite, sericite, and quartz in a K–Na–Al–Si–O–H system, and sulfides in a Fe–S–O–H system. The major and trace elements were calculated by the mass-balance method, showing gains during early alteration and losses during late alteration. The contents of K2O, Na2O, CaO, and LOI varied within the K–Na–Al–Si–O–H system during alteration, while Fe2O3 and MgO were relatively stable. Rare-earth elements (REE) changed from gains to losses alongside the breakdown of accessory minerals, such as large ion lithophile elements (LILE). The Sr and Ba contents exhibited high mobility during sericite-quartz alteration. Most of the low-mobility high-field strength elements (HFSE) were moderately depleted, except for Pb, which was extremely high in anomalous samples. The behavior of trans-transition elements (TRTE) was related to complicated sulfides in the Fe–S–O–H system and was constrained by the parameters of the mineral assemblages and geochemical compositions, temperature, pressure, pH, and fO2. These factors during ore formation that were associated with the extents and intensity of sulfide alteration and gold precipitation can be utilized to evaluate the potential size and scale of an ore-forming hydrothermal system, and is an effective exploration tool for widespread auriferous quartz veins in Archean metamorphic basements.

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Andersson, Joel B. H., Tobias E. Bauer, and Edward P. Lynch. "Evolution of structures and hydrothermal alteration in a Palaeoproterozoic supracrustal belt: Constraining paired deformation–fluid flow events in an Fe and Cu–Au prospective terrain in northern Sweden." Solid Earth 11, no. 2 (April 17, 2020): 547–78. http://dx.doi.org/10.5194/se-11-547-2020.

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Abstract. An approximately 90 km long Palaeoproterozoic supracrustal belt in the northwestern Norrbotten ore province (northernmost Sweden) was investigated to characterize its structural components, assess hydrothermal alteration–structural geology correlations, and constrain a paired deformation–fluid flow evolution for the belt. New geological mapping of five key areas (Eustiljåkk, Ekströmsberg, Tjårrojåkka, Kaitum West, and Fjällåsen–Allavaara) indicates two major compressional events (D1 and D2) have affected the belt, with each associated with hydrothermal alteration types typical for iron oxide–apatite and iron oxide Cu–Au systems in the region. Early D1 generated a regionally distributed, penetrative S1 foliation and oblique reverse shear zones that show a southwest-block-up sense of shear that formed in response to NE–SW crustal shortening. Peak regional metamorphism at epidote–amphibolite facies broadly overlaps with this D1 event. Based on overprinting relationships, D1 is associated with regional scapolite ± albite, magnetite + amphibole, and late calcite alteration of mafic rock types. These hydrothermal mineral associations linked to D1 structures may form part of a regionally pervasive evolving fluid flow event but are separated in this study by crosscutting relationships. During D2 deformation, folding of S0–S1 structures generated F2 folds with steeply plunging fold axes in low-strain areas. NNW-trending D1 shear zones experienced reverse dip-slip reactivation and strike-slip-dominated movements along steep, E–W-trending D2 shear zones, producing brittle-plastic structures. Hydrothermal alteration linked to D2 structures is a predominantly potassic–ferroan association comprising K-feldspar ± epidote ± quartz ± biotite ± magnetite ± sericite ± sulfides. Locally, syn- or post-tectonic calcite is the main alteration mineral in D2 shear zones that intersect mafic rocks. Our results highlight the importance of combining structural geology with the study of hydrothermal alterations at regional to belt scales to understand the temporal–spatial relationship between mineralized systems. Based on the mapping results and microstructural investigations as well as a review of earlier tectonic models presented for adjacent areas, we suggest a new structural model for this part of the northern Fennoscandian Shield. The new model emphasizes the importance of reactivation of early structures, and the model harmonizes with tectonic models presented by earlier workers based mainly on petrology of the northern Norrbotten area.

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Jin, Shiyun, Ziyin Sun, and Aaron C. Palke. "Iron oxide inclusions and exsolution textures of rainbow lattice sunstone." European Journal of Mineralogy 34, no. 2 (March 28, 2022): 183–200. http://dx.doi.org/10.5194/ejm-34-183-2022.

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Abstract. Iron oxide inclusions and exsolution lamellae in rainbow lattice sunstone (RLS) from Harts Range, Australia, are examined using optical and electron microscopy and single-crystal X-ray diffraction (SC-XRD). Laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS) analyses show a bulk composition of An1.4Ab14.8Or83.0Cn0.8 with < 200 ppmw (parts per million weight) of Fe. Two stages of exsolution can be identified in RLS from the bimodal distribution in the size and shape of the exsolution lamellae. Micron-scaled Albite-twinned oligoclase spindles (An27Ab72Or1) first exsolved at ∼ 650 ∘C were followed by nanoscaled Pericline-twinned albite films (∼ Ab100) below 500 ∘C that create adularescence. The albite films inherited and preserved the monoclinic tetrahedral framework of the orthoclase matrix (An0.3Ab11.5Or87.3Cn0.9) as further ordering was completely inhibited by coherent-interface strain after exsolution. All the exsolution lamellae are pristine and strain-controlled with no signs of any deuteric or hydrothermal alteration, indicating the iron in the magnetite inclusions was not introduced by an external fluid. The magnetite inclusions nucleated around the same time as the exsolution of oligoclase spindles likely due to the reduction of Fe3+ to Fe2+ in the feldspar lattice. Magnetite films following the specific crystallographic orientation relationship (COR) of {111}Mt∥{100}Or and 11‾0Mt∥001Or grew to extraordinarily large sizes due to the near perfect lattice match at the interface with the orthoclase host. Some thinner magnetite films were oxidized into hematite during weathering of the host rock. RLS reveals a new mechanism for the formation of the flaky hematite inclusions in feldspars, which may explain the enigmatic origin of aventurescence observed in many other sunstones and red-clouded feldspars.

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33

Kamali, Amin Allah, Mohsen Moayyed, Nasir Amel, Fadaeian Mohammad, Marco Brenna, Benoit M. Saumur, and José Francisco Santos. "Mineralogy, mineral chemistry and thermobarometry of post-mineralization dykes of the Sungun Cu–Mo porphyry deposit (Northwest Iran)." Open Geosciences 12, no. 1 (September 23, 2020): 764–90. http://dx.doi.org/10.1515/geo-2020-0009.

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AbstractThe Sungun copper–molybdenum porphyry deposit is located in the north of Varzaghan, northwestern Iran. The Sungun quartz-monzonite is the oldest mineralized intrusive body in the region and was emplaced during the Early Miocene. Eight categories of the late and unmineralized dykes, which include quartz diorite, gabbrodiorite, diorite, dacite, microdiorite and lamprophyre (LAM), intrude the ore deposit. The main mineral phases in the dykes include plagioclase, amphibole and biotite, with minor quartz and apatite and secondary chlorite, epidote, muscovite and sericite. The composition of plagioclase in the quartz diorite dykes (DK1a, DK1b and DK1c) varies from albite-oligoclase to andesine and oligoclase to andesine; in the diorite, it varies from andesine to labradorite; in the LAM, from albite to oligoclase; and in the microdiorite (MDI), it occurs as albite. Amphibole compositions are consistent with classification as hornblende or calcic amphibole. Based on their AlIV value (less than 1.5), amphibole compositions are consistent with an active continental margin affinity. The average percentage of pistacite (Ps) in epidotes formed from alteration of plagioclase and ferromagnesian minerals is 27–23% and 25–30%, respectively. Thermobarometric studies based on amphibole and biotite indicate approximate dyke crystallization temperature of 850–750℃, pressure of 231–336 MPa and high fO2 (>nickel-nickel-oxide buffer). The range of mineral compositions in the postmineralization dyke suite is consistent with a genetic relationship with the subduction of the Neotethys oceanic crust beneath the continental crust of the northwest part of the Central Iranian Structural Zone. Despite the change from calc-alkaline to alkaline magmatism, the dykes are likely related to the late stages of magmatic activity in the subduction system that also generated the porphyry deposit.

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Witt, W. K. "Porphyry intrusions and albitites in the Bardoc–Kalgoorlie area, Western Australia, and their role in Archean epigenetic gold mineralization." Canadian Journal of Earth Sciences 29, no. 8 (August 1, 1992): 1609–22. http://dx.doi.org/10.1139/e92-127.

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Minor intrusions in the Menzies – Kambalda greenstone belt of the Archean Eastern Goldfields Province, Western Australia, range from quartz–feldspar porphyry to plagioclase–hornblende porphyry. The porphyries display enrichment of mobile and incompatible elements (K to Zr) and depletion of relatively compatible elements, with negative Nb, P, and Ti anomalies, on mid-ocean-ridge basalt-normalized spidergrams. The composition and timing of emplacement of the porphyries are consistent with a genetic relationship with spatially related granitoids. Porphyries occur in 30% of gold mines in the Menzies–Kambalda belt. The association appears to be largely structural, since both the intrusions and the mineralizing fluids exploit zones of weaknesses, such as lithological contacts and shear zones. Porphyries have been modified to varying degrees by hydrothermal alteration, especially pervasive albitization. Textural evidence indicates that secondary albite and associated sodic amphibole formed late in the deformation history of the greenstones and were broadly contemporaneous with secondary phyllosilicate, carbonate and sulphide minerals related to gold mineralization. Recent studies in the Alleghany district of California suggest the initial rock composition may critically influence the nature of alteration associated with gold mineralization. Therefore, albitization of porphyries may be caused by the same hydrothermal fluids that deposit gold and produce potassic alteration in mafic rocks.

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35

Sutton, S. J., and J. B. Maynard. "Petrology, mineralogy, and geochemistry of sandstones of the lower Huronian Matinenda Formation: resemblance to underlying basement rocks." Canadian Journal of Earth Sciences 30, no. 6 (June 1, 1993): 1209–23. http://dx.doi.org/10.1139/e93-103.

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Bulk chemistry, mineralogy, mineral chemistry, cathodoluminescence characteristics, and textural data are used to constrain provenance and the role of postdepositional alteration processes in sandstones of the lower Huronian Matinenda Formation. Samples studied are from the Elliot Lake – Blind River and Agnew Lake areas, which experienced subgreenschist and biotite-grade greenschist metamorphism, respectively. Both areas, but particularly the lower grade area, contain some K-rich samples, with much of the K in detrital-appearing K-feldspar. In places K-feldspar is partially replaced by potassic mica. Plagioclase (mostly albite) is rare in the Elliot Lake – Blind River samples, and only common along a few horizons in the Agnew Lake section. It is suggested that the predominance of K-feldspar over plagioclase and the high K/Na ratios indicate a K-rich source area and in particular a weathered granite source. Framework mineralogy is found to be similar to material reported from sub-Matinenda weathered granite. The abundance of fine-grained micaceous matrix within the Matinenda varies considerably among samples, and the composition of the mica varies, correlating strongly with bulk chemistry. Some matrix has clearly been generated by alteration of framework K-feldspar. Feldspar alteration may have liberated K that was carried to the underlying regolith where it was fixed by weathering-product clay minerals. Fluids involved in alteration do not appear to have pervasively affected the Matinenda in either the Elliot Lake – Blind River or the Agnew Lake area.

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Scheepers, R., R. D. O'Brien, and A. E. Schoch. "An occurrence of bavenite in the Cape Granite Suite, southwestern Cape Province, South Africa, and its implication on the formation of the host pegmatite." South African Journal of Geology 120, no. 2 (June 1, 2017): 223–30. http://dx.doi.org/10.25131/gssajg.120.2.223.

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Abstract Bavenite, (Ca4[(Al,Be)4(Si9(O,OH)26-n)](OH)2+n), is present in a pegmatite of the Paarl Pluton, a metaluminous I-type granite of Late Precambrian age. We are not aware of any other previous description of a beryllium mineral occurrence in the Cape Granite Suite. The pegmatite consists essentially of quartz and microcline microperthite together with albite, calcite and fluorite. A hydrothermal alteration assemblage of epidote, chlorite and bavenite occurs in vugs and veins within the pegmatite. Stilbite, which is stable below 170ºC, is also present, but not texturally related to the alteration assemblage. Microthermometric analyses and mineral chemistry of associated minerals elucidate the conditions of formation for the bavenite. According to primary fluid inclusions in the cores of euhedral quartz, the minimum temperature of crystallization of the pegmatite is 450ºC. Homogenization temperatures of later fluids indicate a minimum temperature of 210ºC for the main hydrothermal event. Chlorite geothermometry yields crystallization temperatures around 320ºC. The bavenite formed between 210ºC and 320ºC, at a pressure of less than 2 kbar.

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37

Morad, S., M. Sirat, M. A. K. El-Ghali, and H. Mansurbeg. "Chloritization in Proterozoic granite from the Äspö Laboratory, southeastern Sweden: record of hydrothermal alterations and implications for nuclear waste storage." Clay Minerals 46, no. 3 (September 2011): 495–513. http://dx.doi.org/10.1180/claymin.2011.046.3.495.

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AbstractHydrothermal alteration of Proterozoic granitic rocks in the Äspö underground laboratory, southestern Sweden, resulted in the formation of chlorite with large variations in textural and chemical characteristics, which reflect differences in formation temperatures, fluid composition, and reaction mechanisms. The mineral assemblage associated with chlorite, including Ca-Al silicates (prehnite, pumpellyite, epidote, and titanite), Fe-oxides, calcite, albite and K-feldspar, suggests that chloritization occurred at temperatures of between 200–350°C during various hydrothermal events primarily linked to magmatism and rock deformation. Petrographic and electron microprobe analyses revealed that chlorite replaced biotite, amphibole and magnetite, and hydrothermal chlorite phases filled fractures and vugs in the granitic rocks. While fracture-filling chlorite reduces fracture permeability, chloritization reactions in the host granite resulted in the formation of new localized microporosity that should thus be taken into consideration when evaluating the safety of the granitic basement rocks as a repository for nuclear waste. It is also important to take into account that similar alteration reactions may occur at the site of stored nuclear waste where temperatures in excess of 100°C might be encountered.

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Rae, D. A., and A. D. Chambers. "Metasomatism in the North Qôroq centre, South Greenland: cathodoluminescence and mineral chemistry of alkali feldspars." Transactions of the Royal Society of Edinburgh: Earth Sciences 79, no. 1 (1988): 1–12. http://dx.doi.org/10.1017/s0263593300014061.

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ABSTRACTThe North Qôroq centre consists of a number of units of syenite, all undersaturated, with later units in sharp intrusive contact with earlier ones. Chemical and mineralogical characteristics have been determined by primary crystal-silicate liquid equilibria and also later, extensive, metasomatic alteration probably involving an alkali-rich aqueous phase. Cathodoluminescence studies on feldspars, the dominant phase present, reveal the development of red-luminescing albite in all the rocks affected by a late-stage fluid phase in contrast with the blue luminescence shown by unaltered perthites. Spectral and chemical investigation of the feldspars confirms earlier views that red luminescence is caused by Fe3+, an impurity in the feldspar structure, but also indicates that, for red luminescence to be seen, the blue luminescent peak must be greatly reduced or absent. The cause of the blue luminescence is less obvious but may well be related to an oxygen defect centre. Such a centre is apparently absent in red-luminescing albites and hence not formed during growth involving late-stage fluids. The fluids evolved from highly peralkaline, undersaturated magmas and metasomatised less evolved syenites forming feldspathoids, particularly sodalite. Once equilibrium had been attained the fluid behaved principally as a passive phase on its passage through the rocks, aiding the unmixing of the alkali feldspars.

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Jensen, Aage. "The Bjergebakke dyke - a kullaite from Bomholm." Bulletin of the Geological Society of Denmark 37 (April 10, 1989): 123–40. http://dx.doi.org/10.37570/bgsd-1988-37-11.

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The Bjergebakke dyke is a 2-3 m wide dyke trending northwest and cutting through the Almindingen granite in the central part of Bomholm. Along the contact there is an approximately 1 cm thick white zone consisting almost exclusively of albite, and the dyke has suffered from later autometasomatic alteration, mainly albitisation. The dyke consists of feldspar, al bite as well as potassium feldspar, chlorite, mica and opaque minerals, mainly titanomagnetite, beside traces of calcite and amphibole. The composition of the feldspars, chlorite, mica and titanomagnetite have been determined by electron microprobe analysis. Whole rock analyses, major elements as well as trace elements were carried out in two profiles across the dyke with sample distances of 30 and 25 cm respectively. It is concluded that the present distribution of elements is due to autometasomatic alteration and that any original magmatic differentiation can no longer be seen. Both the direction of and the mineralogical and chemical composition of the Bjergebakke dyke is quite similar to that of the kullaites in Scania, but whereas the dykes in the Precambrian of Bornholm are considered to be Precambrian, the kullaites have been considered post-Silurian. Age determinations of these rocks are being undertaken.

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40

Kontonikas-Charos, Alkis, Cristiana L. Ciobanu, Nigel J. Cook, Kathy Ehrig, Roniza Ismail, Sasha Krneta, and Animesh Basak. "Feldspar mineralogy and rare-earth element (re)mobilization in iron-oxide copper gold systems from South Australia: a nanoscale study." Mineralogical Magazine 82, S1 (February 28, 2018): S173—S197. http://dx.doi.org/10.1180/minmag.2017.081.040.

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ABSTRACTNanoscale characterization (TEM on FIB-SEM-prepared foils) was undertaken on feldspars undergoing transformation from early post-magmatic (deuteric) to hydrothermal stages in granites hosting the Olympic Dam Cu-U-Au-Ag deposit, and from the Cu-Au skarn at Hillside within the same iron-oxide copper-gold (IOCG) province, South Australia. These include complex perthitic textures, anomalously Ba-, Fe-, or REE-rich compositions, and REE-flourocarbonate + molybdenite assemblages which pseudomorph pre-existing feldspars. Epitaxial orientations between cryptoperthite (magmatic), patch perthite (dueteric) and replacive albite (hydrothermal) within vein perthite support interface-mediated reactions between pre-existing alkali-feldspars and pervading fluid, irrespective of micro-scale crystal morphology. Such observations are consistent with a coupled dissolution-reprecipitation reaction mechanism, which assists in grain-scale element remobilization via the generation of transient interconnected microporosity. Micro-scale aggregates of hydrothermal hyalophane (Ba-rich K-feldspar), crystallizing within previously albitized areas of andesine, reveal a complex assemblage of calc-silicate, As-bearing fluorapatite and Fe oxides along reaction boundaries in the enclosing albite-sericite assemblage typical of deuteric alteration. Such inclusions are good REE repositories and their presence supports REE remobilization at the grain-scale during early hydrothermal alteration. Iron-metasomatism is recognized by nanoscale maghemite inclusions within ‘red-stained’ orthoclase, as well as by hematite in REE-fluorocarbonates, which reflect broader-scale zonation patterns typical for IOCG systems. Potassium-feldspar from the contact between alkali-granite and skarn at Hillside is characterized by 100–1000 ppm REE, attributable to pervasive nanoscale inclusions of calc-silicates, concentrated along microfractures, or pore-attached. Feldspar replacement by REE-fluorcarbonates at Olympic Dam and nanoscale calc-silicate inclusions in feldspar at Hillside are both strong evidence for the role of feldspars in concentrating REE during intense metasomatism. Differences in mineralogical expression are due to the availability of associated elements. Lattice-scale intergrowths of assemblages indicative of Fe-metasomatism, REE-enrichment and sulfide deposition at Olympic Dam are evidence for a spatial and temporal relationship between these processes.

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41

Jenkins, Cecilia L., Pierre Trudel, and Guy Perrault. "Progressive hydrothermal alteration associated with gold mineralization of the Zone 1 intrusion of the Callahan property, Val-d'Or region, Quebec." Canadian Journal of Earth Sciences 26, no. 12 (December 1, 1989): 2495–506. http://dx.doi.org/10.1139/e89-212.

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The Zone 1 intrusion of the Callahan property, Val-d'Or, Quebec, is a relatively small (0.045 km2), pretectonic to syntectonic trondhjemitic mass that has been altered to varying degrees by progressive hydrothermal alteration. The entire intrusion is gold enriched, and the degree of mineralization is proportional to the degree of alteration. Examination of drill core reveals that visible colour variations are related to mineralogic and chemical alteration. Three degrees of alteration are identified: least, medium, and most-altered. The least-altered facies has a green–grey colour, whereas the medium-altered facies has a pale grey colour and the most-altered facies has a cream–white colour. As the intensity of alteration increases, the amount of albite, carbonate, and pyrite increases and the amount of phengite decreases. These progressive, mineralogic changes are correlated chemically to increases in Na2O, CO2, and S and to a decrease in K2O. The median gold values for least-, medium-, and most-altered trondhjemite are 42, 148, and 158 ppb, respectively, and the average gold values (excluding highly anomalous values) are 85, 172, and 188 ppb, respectively, indicating that gold enrichment is already advanced at the medium intensity of alteration. Despite its weak enrichment, tungsten is the most anomalous trace element of the typically gold-associated elements in lode deposits and is, therefore, of special interest. Gold, found principally in the medium- and most-altered facies, is most commonly observed as free grains in the gangue. It may also be associated with pyrite and, to a much lesser extent, with tellurides. The majority of the free gold grains have an estimated diameter between 20 and 60 μm, and their average composition is 95 wt.% Au and 5 wt.% Ag. This study and comparisons of the Zone 1 trondhjemitic intrusion with other gold-enriched, felsic intrusions in the Abitibi greenstone belt suggest that elevated sodium (i.e., albitization) and anomalous gold values, relative to barren felsic rocks, should be used to target ore-grade zones within pretectonic to syntectonic felsic intrusions.

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Milovanović, Dragan, Danica Srećković-Batoćanin, Marija Savić, and Dana Popovic. "Petrology of plagiogranite from Sjenica, Dinaridic Ophiolite Belt (southwestern Serbia)." Geologica Carpathica 63, no. 2 (April 1, 2012): 97–106. http://dx.doi.org/10.2478/v10096-012-0008-4.

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Petrology of plagiogranite from Sjenica, Dinaridic Ophiolite Belt (southwestern Serbia)The Sjenica plagiogranite occurs in the southern part of the Dinaridic Ophiolite Belt, 5 km northwest of Sjenica. The main minerals are albite with strongly altered biotite (replaced with chlorite), with occasional amphibole (magnesio hornblende to tschermakite) and quartz. An enclave of fine-grained granitic rocks with garnet grains was noted too. Secondary minerals are calcite and chlorite (daphnite). Major, trace and REE geochemistry coupled with field observations support a model by which the Sjenica plagiogranite could be formed by fractional crystallization of mantle origin mafic magma in a supra-subduction zone setting. Occurrences of calcite and chlorite nests in the Sjenica plagiogranites revealed that these rocks underwent hydrothermal alteration due to intensive sea water circulation in a sub-sea-floor environment.

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King, R. W., and R. Kerrich. "Fluorapatite fenitization and gold enrichment in sheeted trondhjemites within the Destor–Porcupine fault zone, Taylor Township, Ontario." Canadian Journal of Earth Sciences 24, no. 3 (March 1, 1987): 479–502. http://dx.doi.org/10.1139/e87-049.

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Pronounced fluorapatite mineralization is present in sheeted trondhjemites near Timmins. The trondhjemites intrude a deformed ultramafic to Fe-tholeiite volcanic sequence disposed in the structural hanging wall of the Destor–Porcupine Fault, and they bound a domain of high-grade gold ore. Spinifex-textured ultramafic flows record variable intensities of secondary alteration to a carbonate–Cr-muscovite assemblage. They are characterized by chondritic Al2O3/TiO2 ratios (19 ± 1.7), enhanced Cr (1570–2090 ppm) and Ni (470–1070 ppm), together with low levels of the incompatible elements Ta, Nb, and Th.Fresh quartz–oligoclase trondhjemitic intrusions are compositionally coherent with respect to SiO2 (average 63 wt.%), Al2O3 (16.3 wt. %), and Na2O (6.7 wt. %), as well as to the alteration-insensitive elements V, Sc, Zr, and Hf. Whole-rock δ18O values of 10.0–10.6‰, combined with "magmatic" quartz–feldspar (0.8–0.9‰), signify that these are primary high-18O magmas, likely derived by partial melting of 18O-enriched mafic granulites. Albitic trondhjemites are characterized by enhanced Na2O (10.8 wt. %) and are systematically enriched by ~1‰ relative to fresh counterparts, due to a preferential positive 18O shift of albite, resulting in negative quartz–feldspar. Sodium enrichment coupled with isotopic disturbance is attributed to low-temperature spilitization in the presence of marine water.A domain of high-grade gold ore is focussed in an intensely silicified unit. The ore is composed of quartz, feldspar, muscovite, carbonate, graphite, pyrite, molybdenite, and gold, with corresponding pronounced enrichments of Si, K, Rb, Ba, Cs, S, C, As, Sb, Pb, and Mo. The lithology is compositionally diverse but uniform with respect to Al2O3/TiO2 (17–27) and Ti/Zr (60–73). These features, combined with variably elevated Cr (50–955 ppm) and Ni (60–570), low contents of the incompatible elements, and a flat REE distribution, collectively indicate Fe-tholeiite and basaltic komatiite precursors. The silicified unit is bounded by trondhjemites overprinted by a secondary muscovite–Fe-dolomite alteration assemblage, with associated anomalies of CO2, S, As, Sb, Mo, and Pb. Quartz is isotopically uniform (δ18O = 14.1 ± 0.2‰ (1σ), n = 15) throughout the diverse lithologies overprinted by alteration linked to gold mineralization. Quartz is shifted ~+3‰ and albite ~−1‰ relative to fresh trondhjemites, such that Δquartz–feldspar = 1.8 to 2.6‰ in ore. Fluids implicated in gold mineralization were characterized by ambient temperatures of 330 ± 20 °C and by [Formula: see text]. Carbon-isotope compositions of hydrothermal ferroan dolomite are constrained at δ13C = −2.5 ± 0.8‰, but they are systematically heavier in graphitic rocks. δCgraphite averages −20.8‰.Fluorapatite occurs as megacrysts superimposed on trondhjemites and as microveins in a narrow domain cospatial with the Destor–Porcupine Fault. Its modal abundance correlates directly with P2O5 and F, which attain levels of 6.8 wt.% and 6800 ppm, respectively. Fluorapatite is close to end-member composition and possesses extremely enhanced REE abundances: 87Sr/86Sr = 0.7012, a value similar to that for contemporaneous mantle. Rocks have been extensively stripped of Si, K, Na, and Al in domains of fluorapatite, signifying a process allied to fenitization.

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Gisbert, Guillem, Fernando Tornos, Emma Losantos, Juan Manuel Pons, and Juan Carlos Videira. "Vectors to ore in replacive volcanogenic massive sulfide (VMS) deposits of the northern Iberian Pyrite Belt: mineral zoning, whole rock geochemistry, and application of portable X-ray fluorescence." Solid Earth 12, no. 8 (August 20, 2021): 1931–66. http://dx.doi.org/10.5194/se-12-1931-2021.

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Abstract. In this work we have performed a detailed study of vectors to ore to a representative volcanic-rock-hosted replacive volcanogenic massive sulfide (VMS) deposit located in the northern Iberian Pyrite Belt (Spain), the Aguas Teñidas deposit. The investigated vectors include the following: (1) mineralogical zoning, (2) host sequence characterization and mineralized unit identification based on whole rock geochemistry discrimination diagrams, (3) study of the characteristics and behaviour of whole rock geochemical anomalies around the ore (e.g. alteration-related compositional changes, characteristics and extent of geochemical halos of indicative elements such as Cu, Zn, Pb, Sb, Tl, and Ba around the deposit), and (4) application of portable X-ray fluorescence (p-XRF) analysis to the detection of the previous vectors. In the footwall, a concentric cone-shaped hydrothermal alteration zone bearing the stockwork passes laterally, from core to edge, from quartz (only local) to chlorite–quartz, sericite–chlorite–quartz, and sericite–quartz alteration zones. The hydrothermal alteration is also found in the hanging wall despite being tectonically allochthonous to the orebody: a proximal sericite alteration zone is followed by a more distal albite-rich one. Whole rock major elements show an increase in alteration indexes (e.g. AI, CCPI) towards the mineralization, a general SiO2 enrichment, and FeO enrichment as well as K2O and Na2O depletion towards the centre of the hydrothermal system, with MgO showing a less systematic behaviour. K2O and Na2O leached from the centre of the system are transported and deposited in more external areas. Copper, Pb, and Zn produce proximal anomalies around mineralized areas, with the more mobile Sb, Tl, and Ba generating wider halos. Whereas Sb and Tl halos form around all mineralized areas, Ba anomalies are restricted to areas around the massive sulfide body. Our results show that proposed vectors, or adaptations designed to overcome p-XRF limitations, can be confidently used by analysing unprepared hand specimens, including the external rough curved surface of drill cores. The data presented in this work are not only applicable to VMS exploration in the Iberian Pyrite Belt, but on a broader scale they will also contribute to improving our general understanding of vectors to ore in replacive-type VMS deposits.

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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.

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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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46

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.

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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.

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47

Petrounias, Petros, Panagiota Giannakopoulou, Aikaterini Rogkala, Panagiotis Stamatis, Paraskevi Lampropoulou, Basilios Tsikouras, and Konstantin Hatzipanagiotou. "The Effect of Petrographic Characteristics and Physico-Mechanical Properties of Aggregates on the Quality of Concrete." Minerals 8, no. 12 (December 8, 2018): 577. http://dx.doi.org/10.3390/min8120577.

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This paper examines the effect of the aggregate type on concrete strength, and more specifically, how the petrographic characteristics of various aggregate rocks as well as their physico-mechanical properties influences the durability of C 25/30 strength class concrete. The studied aggregate rocks were derived from Veria-Naousa and Edessa ophiolitic complexes as well as granodiorite and albitite rocks from their surrounding areas in central Macedonia (Greece). Concretes were produced with constant volume proportions, workability, mixing and curing conditions using different sizes of each aggregate type. Aggregates were mixed both in dry and water saturated states in concretes. Six different types of aggregates were examined and classified in three district groups according to their physicomechanical properties, petrographic characteristics and surface texture. The classification in groups after the concrete compressive strength test verified the initial classification in the same three groups. Group I (ultramafic rocks) presented the lowest concrete strengths, depending on their high alteration degree and the low mechanical properties of ultramafic aggregates. Group II (mafic rocks and granodiorite) presented a wide range of concrete strengths, depending on different petrographic characteristics and mechanical properties. Group III (albite rocks) presented the highest concrete strengths, depending on their lowest alteration degree and their highest mechanical properties. Therefore, mineralogy and microstructure of the coarse aggregates affected the final strength of the concrete specimens.

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48

LOPES, ANGELA PACHECO, and LÉO AFRANEO HARTMANN. "Geoquímica de Rochas Metabasálticas da Mina da Palma, Bloco São Gabriel, Escudo Sul-rio-grandense: Um Possível Platô Oceânico." Pesquisas em Geociências 30, no. 1 (June 30, 2003): 27. http://dx.doi.org/10.22456/1807-9806.19577.

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The Mina da Palma oceanic plateau is described for the first time in the São Gabriel Block, southern Brazilian Shield. It is composed mostly of metabasalts, marbles and metachert. Two deformational events are recognized in the Palma region, thrust faulting followed by dextral subvertical shearing. The rocks were metamorphosed in the greenschist facies, as shown by the dominant mineral assemblage albite-actinolite-chlorite-epidote-opaques. Metamorphic alteration was intense, because only a few relicts of the original magmatic textures are preserved, such as flow structure of amphibole and plagioclase. In spite of intense alteration during metamorphism, geochemical studies show that the chemical composition of many basalts is still preserved. The metabasalts are transitional tholeiite/alkaline and reflect intraplate conditions of formation. The tectonic environment was identified by field relations, such as predominance of basalts and small volume of marble and chert and minor clastic sedimentary rocks. The tectonic environment of formation is reflected in the geochemistry, particularly in multi-element spidergrams, because no significant Nb anomaly is observed in the least altered samples.Previous investigations showed the presence of an island-arc basaltic-andesitic association in the Palma region, which indicated that the geological unit contains one oceanic association and one active plate margin association. This is possibly the first description of remnants of an oceanic plateau in the Brazilian Shield.

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49

Byrne, Kevin, Robert B. Trumbull, Guillaume Lesage, Sarah A. Gleeson, John Ryan, Kurt Kyser, and Robert G. Lee. "Mineralogical and Isotopic Characteristics of Sodic-Calcic Alteration in the Highland Valley Copper District, British Columbia, Canada: Implications for Fluid Sources in Porphyry Cu Systems." Economic Geology 115, no. 4 (June 1, 2020): 841–70. http://dx.doi.org/10.5382/econgeo.4740.

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Abstract The Highland Valley Copper porphyry Cu (±Mo) district is hosted in the Late Triassic Guichon Creek batholith in the Canadian Cordillera. Fracture-controlled sodic-calcic alteration is important because it forms a large footprint (34 km2) outside of the porphyry Cu centers. This alteration consists of epidote ± actinolite ± tourmaline veins with halos of K-feldspar–destructive albite (1–20 XAn) ± fine-grained white mica ± epidote. The distribution of sodic-calcic alteration is strongly influenced by near-orthogonal NE- and SE-trending fracture sets and by proximity to granodiorite stocks and porphyry dikes. Multiple stages of sodic-calcic alteration occurred in the district, which both pre- and postdate Cu mineralization at the porphyry centers. The mineral assemblages and chemical composition of alteration minerals suggest that the fluid that caused sodic-calcic alteration in the Guichon Creek batholith was Cl bearing, at near-neutral pH, and oxidized, and had high activities of Na, Ca, and Mg relative to propylitic and fresh-rock assemblages. The metasomatic exchange of K for Na, localized removal of Fe and Cu, and a paucity of secondary quartz suggest that the fluid was thermally prograding in response to magmatic heating. Calculated δ18Ofluid and δDfluid values of mineral pairs in isotopic equilibrium from the sodic-calcic veins and alteration range from 4 to 8‰ and −20 to −9‰, respectively, which contrasts with the whole-rock values for least altered magmatic host rocks (δ18O = 6.4–9.4‰ and δD = −99 to −75‰). The whole-rock values are suggested to reflect residual magma values after D loss by magma degassing, while the range of hydrothermal minerals requires a mixed-fluid origin with a contribution of magmatic water and an external water source. The O-H isotope results favor seawater as the source but could also reflect the ingress of Late Triassic meteoric water. The 87Sr/86Srinital values of strongly Na-Ca–altered rocks range from 0.703416 to 0.703508, which is only slightly higher than the values of fresh and potassic-altered rocks. Modeling of those data suggests the Sr is derived predominantly from a magmatic source, but the system may contain up to 3% seawater Sr. Supporting evidence for a seawater-derived fluid entrained in the porphyry Cu systems comes from boron isotope data. The calculated tourmaline δ11Bfluid values from the sodic-calcic domains reach 18.3‰, which is consistent with a seawater-derived fluid source. Lower tourmaline δ11Bfluid values from the other alteration facies (4–10‰) suggest mixing between magmatic and seawater-derived fluids in and around the porphyry centers. These results imply that seawater-derived fluids can infiltrate batholiths and porphyry systems at deep levels (4–5 km) in the crust. Sodic ± calcic alteration may be more common in rocks peripheral to porphyry Cu systems hosted in island-arc terranes and submarine rocks than currently recognized.

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50

Andayany, Helda, and Josephus Ronny Kelibulin. "Characteristics Of Minerals With Spectroskopic IR At The Gold Mining Area Of Botak Mountain." Jurnal Fisika Indonesia 22, no. 2 (April 16, 2020): 7. http://dx.doi.org/10.22146/jfi.v22i2.41529.

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There are three rock samples that have been taken from the gold mining area of Botak mountain. The rock samples were then analyzed with spectroscopic IR to estimate the characteristic of mineral in the area. Analysis results indicate that the type of mineral found in rock samples 2 is dominated by Kaolinite, Organic Carbon, Palygorskite and Quartz. So it can be estimate the type of rock contained in that area is Quartzite. The analysis result of mineral type analysis on rock samples 1 dan 3 have similarities that is Kaolinite, Organic Carbon, Palygorskite, and Albite. So it can be estimate that the other types of rock in the area are Andesite and Limestone. The existence of Andesit and Limestone shows that there has been alteration and hydrothermal mineralization from volcanic origin rock. So it can be estimate that these rocks are the bearing rocks and hosted rocks of base metals and gold. Whereas the quartzite is a bond mineral from gold carrying rocks

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