Academic literature on the topic 'Precious opal deposits'

Silica sinters forming at the Wairakei geothermal power plant in New Zealand are composed of noncrystalline opal-A that deposited rapidly from cooling geothermal liquids flashed to atmosphere. The sinter is laminated with alternating layers of variably compacted silicified filamentous microbes encased by chains of fused silica microspheres. Microscopic inspection of bonanza quartz vein samples from the Buckskin National low-sulfidation epithermal precious metal deposit in Nevada showed that colloform bands in these veins exhibit relic microsphere textures similar to those observed in the silica sinters from the Wairakei power plant. The textural similarity suggests that the colloform bands were originally composed of noncrystalline opal-A that subsequently recrystallized to quartz. The colloform bands contain dendrites of electrum and naumannite that must have grown in a yielding matrix of silica microspheres deposited at the same time as the ore minerals, implying that the noncrystalline silica exhibited a gel-like behavior. Quartz bands having other textural characteristics in the crustiform veins lack ore minerals. This suggests that ore deposition and the formation of the colloform bands originally composed of compacted microspheres of noncrystalline silica are genetically linked and that ore deposition within the bonanza veins was only episodic. Supersaturation of silica and precious metals leading to the formation of the colloform bands may have occurred in response to transient flashing of the hydrothermal liquids. Flashing of geothermal liquids may thus represent a key mechanism in the formation of bonanza precious metal grades in low-sulfidation epithermal deposits.

AbstractSzklary Massif is situated about 60 km from Wrocław (southwestern Poland) and around 7 km from Ząbkowice Śląskie. The history of raw materials in this region started in the fifteenth century with the discovery of precious minerals like chrysoprase, chalcedony, and opal. The exploitation of nickel ore in this region started in the nineteenth century and was conducted with few stops until 1983. The remaining 17.21 mln mg of ore with 125,000 mg of nickel might be a chance to satisfy rising demand for raw materials used to develop electromobility. One of the crucial aspects regarding possible investment is the processing of ore. The pilot tests show the efficient use of heap leaching. The authors provide the future project in Szklary within the framework of circular economy.

ABSTRACTChemical and structural characterization of four representative samples of an ore deposit located in the eastern of Hidalgo State was carried out. According with the results, it could be appreciate some areas showing silicified zones with abundant amounts of disseminated pyrites that are part of a rock unit from early Jurassic consisting in inter - bedded black shales and sandstones. Thus, the contents of base metal were greater than 30 ppm Zn and 9 ppm Cu. Chemical analysis of rock gave the following results; 82 ppm of Ba, 1.64 % Wt. Fe, 0.08 % Wt. Ti, 40.8 % Wt. Si, 20 ppm of Ce, 2.2 ppm Co, 30 ppm Cr, 2.7 ppm Cs, 0.9 ppm Er, 2.5 ppm Ga, 1.6 ppm Gd , 1.5 ppm Ge, 9 ppm La, 71 ppm Li, 104 ppm Mn, 10 ppm Nd , 17 ppm Rb, 2 ppm Se, 9 ppm Sr, 10 ppm Ta, 6 ppm Te, 28 ppm V, 9 ppm Y, and 0.7 ppm Yb, among others. Finally, the values found for precious metals, were; Au < 0.02 ppm, Pd <0.05 ppm, Pt <0.05 ppm. It was inferred that the low content of base metals in outcrop studied, are due to the alteration of the black shales. According to these results, we can consider a stratiform – type mineralization of Pb-Zn which could be prospective for SEDEX – Type deposit. By means of XRD, it was possible to identify; pyrite, chalcopyrite, pyrrhotite, and minor amounts of sphalerite and Co -Ni arsenide.

High-grade ores in low-sulfidation epithermal precious metal deposits include banded quartz veins that contain gold dendrites. The processes by which dendrite growth takes place have been subject to debate for decades, especially given that these deposits are known to form from dilute thermal liquids that contain only trace amounts of gold. It is shown here that growth of gold dendrites in epithermal veins at the McLaughlin deposit in California (western USA) originally took place within bands of gel-like noncrystalline silica. The gel provided a framework for the delicate dendrites to form. The high permeability of the gel allowed the diffusion and advection of gold from the thermal liquids flowing across the top of the silica layers to the sites of crystal growth within the gel. Over time, the gel hardened to form opal-AG. This silica phase is thermodynamically unstable and recrystallized to quartz that has a distinct mosaic texture.