Preliminary report on the geology of the Sedalia Mine area and its Proterozoic deposits of base-metal sulfides and gahnite, Chaffee County, Colorado

1984 ◽  
Author(s):  
D.M. Sheridan ◽  
W.H. Raymond
Keyword(s):  
Base Metal ◽  
Preliminary Report ◽  
Metal Sulfides ◽  
Mine Area ◽  
Base Metal Sulfides

The occurrence of gold in Voia deposit, South Apuseni Mountains, Romania

2021 ◽  
Author(s):  
Elena-Luisa Iatan
Keyword(s):  
Iron Oxides ◽  
Base Metal ◽  
Mineral Assemblage ◽  
Native Gold ◽  
Metal Sulfides ◽  
Volcanic Complex ◽  
Apuseni Mountains ◽  
Base Metal Sulfides ◽  
Mineral Assemblages ◽  
Phyllic Alteration

<p>Voia deposit belongs to the Săcărâmb-Cetraș-Cordurea Miocene volcano-tectonic alignment of the South Apuseni Mountains, Romania. This large volcanic complex represents a Sarmatian-Pannonian magmatic-hydrothemal mega-system of around 5 km<sup>2</sup> with an estimated 3–4 Ma time-space evolution, consisting of seven andesitic volcanic structures grouped in a circle, three subvolcanic andesite-quartz porphyry microdiorite and associated porphyry Cu-Au(Mo), pyrite Ca-Mg skarns and epithermal Au-Ag-Pb-Zn-Cu mineralizations.</p><p>The mineral assemblages of alteration and mineralization processes belong to several mineralized zones on a vertical scale, according to sampling evidence and laboratory studies. HS products are found in the upper part of the structure (300-500 m), with dominant advanced and intermediate argillic alterations and sulfide-sulfate gold-poor veins (pyrite, marcasite, base metal sulfides, Fe-Ti oxides, vuggy quartz, alunite, gypsum, anhydrite). Within the 500-1200 m depth, the HS mineral assemblages gradually decrease in favor of IS and LS products. It is characterized by the coexistence of gold-rich LS assemblage (native gold, base metal sulfide, adularia, sericite-illite, chlorite, carbonates ± anhydrite veins), with the IS assemblage (iron oxides, chalcopyrite, pyrite, quartz, anhydrite). These assemblages overprint the HS mineral associations, resulting in a transition zone characterized by gold - pyrite - chalcopyrite - iron oxides - quartz - anhydrite mineral assemblage characteristic for HS and native gold - pyrite - base metal sulfides - carbonates - quartz mineral assemblage corresponding to IS+LS type.</p><p>Gold is present in all of the identified mineralization forms: porphyry-epithermal Cu-Au, epi-mesothermal carbonate veins with gold - base metal sulfides, quartz veins with pyrite - chalcopyrite - magnetite ± hematite ± anhydrite, anhydrite veins with base metal sulfides and sulfosalts, anhydrite veins with pyrite - anhydrite ± quartz, vuggy quartz (silica residue) with gold-poor pyrite veins and impregnations in porphyry systems.</p><p>Drilling core samples revealed that in Voia deposit, gold is concentrated in chalcopyrite (drills no. 7, 19, 37) along with pyrite - magnetite - hematite - quartz assemblage from the late potassic stage. The major amount of gold associated with chalcopyrite tends to be mainly submicroscopic. Pyrite from anhydrite veins of the early potassic stage ± phyllic alteration is relatively poor in gold (drills no. 1-6, 8-14). However, the highest gold contents are present in pentagonal dodecahedron pyrites (drills no. 33, 38, 39) of pyrite-chalcopyrite-magnetite ± hematite-quartz assemblage from late potassic stage ± phyllic alteration. Pyrite associated with magnetite from anhydrite veins tends to be poor in gold (drills no. 8, 11, 15, 28, 29). A carbonate vein containing gold-bearing base metal sulfides that was intercepted at 960,00-960,30m depth by drill no. 17 is one of the richest in gold.</p><p>Native gold occurs as fine inclusions in ore minerals (5-20 μm). Large irregular grains of native gold (>50 μm) appear at mineral boundaries and along the fissures. The gold color is bright yellow and has a measured Au:Ag ratio of 5:1, suggesting that native gold has been formed at a relatively high temperature.</p><p>Acknowledgments: This work was supported by two Romanian Ministry of Research and Innovation grants: PN-III-P4-ID-PCCF-2016-4-0014 and PN-III-P1-1.2-PCCDI-2017-0346/29.</p>

Laboratory-Based Bacterial Weathering of the Merensky Reef and Its Impact on Platinum Group Mineral Migration

2021 ◽  
Author(s):  
Ling Tan ◽  
Thomas Jones ◽  
Jianping Xie ◽  
Xinxing Liu ◽  
Gordon Southam
Keyword(s):  
Base Metal ◽  
Mineral Dissolution ◽  
Metal Sulfides ◽  
Acidithiobacillus Thiooxidans ◽  
Thin Sections ◽  
Secondary Minerals ◽  
Merensky Reef ◽  
Fe Oxides ◽  
Base Metal Sulfides ◽  
Platinum Group

Abstract Weathering of the Merensky reef was enhanced under laboratory conditions by Fe- and S-oxidizing bacteria: Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans, and Leptospirillum ferrooxidans. These bacteria preferentially colonized pyrrhotite and pyrite, versus pentlandite and chalcopyrite (all of which were common within the rock substrate), promoting weathering. Weathering of base metal sulfides resulted in the precipitation of Fe oxides, Fe phosphate, and elemental sulfur as secondary minerals. Fe pyroxene weathered readily under acidic conditions and resulted in mineral dissolution, while other silicates (orthopyroxene and plagio-clase) precipitated Fe phosphate spherules or coatings on their surface. The deterioration of the platinum group metal (PGM) matrix (base metal sulfides and silicates) and the occurrence of a platinum grain associated with platinum nanoparticles observed in the biotic thin sections demonstrate that biogeochemical acid weathering is an important step in the active release of intact PGM grains. A platinum grain embedded in secondary Fe oxides/phosphate that had settled by gravity within the weathering solution demonstrates that secondary minerals that formed during weathering of PGM-hosting minerals also represent targets in PGM exploration by trapping and potentially slowing PGM migration. Dispersion halos surrounding or occurring downstream from PGM occurrences will likely produce two physical target classes—i.e., grains and colloids—under surficial weathering conditions.

Mineralogical and isotopic studies of base metal sulfides from the Jiawula Ag–Pb–Zn deposit, Inner Mongolia, NE China

2016 ◽  
Vol 115 ◽  
pp. 480-491 ◽  
Author(s):  
Si-Da Niu ◽  
Sheng-Rong Li ◽  
M. Santosh ◽  
De-Hui Zhang ◽  
Zeng-Da Li ◽  
...  
Keyword(s):  
Base Metal ◽  
Inner Mongolia ◽  
Metal Sulfides ◽  
Ne China ◽  
Base Metal Sulfides ◽  
Isotopic Studies

Formation process of sub-micrometer-sized metasomatic platinum-group element-bearing sulfides in a Tahitian harzburgite xenolith

2020 ◽  
Vol 58 (1) ◽  
pp. 99-114
Author(s):  
Norikatsu Akizawa ◽  
Tetsu Kogiso ◽  
Akira Miyake ◽  
Akira Tsuchiyama ◽  
Yohei Igami ◽  
...  
Keyword(s):  
Base Metal ◽  
Formation Process ◽  
Sulfide Inclusion ◽  
Metal Sulfides ◽  
Base Metal Sulfides ◽  
Sulfide Melt ◽  
Platinum Group ◽  
Earth’S Interior ◽  
Micrometer Scale ◽  
Earth's Interior

ABSTRACT Base-metal sulfides (BMSs) are minerals that host platinum-group elements (PGE) in mantle peridotites and significantly control the bulk PGE content. They have been investigated in detail down to the sub-micrometer scale to elucidate PGE behavior in the Earth's interior. Base-metal sulfides are supposedly subjected to supergene and seawater weathering, leading to the redistribution of PGEs at low temperatures. Careful and thorough measurements of BMSs are thus required to elucidate PGE behavior in the Earth's interior. In the present study, a sub-micrometer-sized PGE-bearing sulfide inclusion in a clinopyroxene crystal in a harzburgite xenolith from Tahiti (Society Islands, French Polynesia) was investigated in detail (down to the sub-micrometer scale) using transmission electron microscopy with energy-dispersive X-ray spectroscopy (TEM-EDS). The sulfide inclusion is of carbonatitic metasomatic origin, as it is enveloped by carbonaceous glass, and forms a planar inclusion array with other PGE-bearing sulfide inclusions. The following sulfide phases were identified using TEM-EDS: Fe- and Ni-rich monosulfide solid solutions (MSSs), Fe- and Ni-rich pentlandite, sugakiite, heazlewoodite, chalcopyrite, and Cu-Ir-Pt-Rh-thiospinel (cuproiridsite–malanite–cuprorhodsite). We established the formation process of the metasomatic PGE-bearing sulfide inclusion by considering morphological and mineral characteristics in addition to the chemical composition. A primary MSS first crystallized from metasomatic sulfide melt at ca. 1000 °C, followed by the crystallization of an intermediate solid solution (ISS) below 900 °C. A high-form (high-temperature origin) Fe-rich pentlandite simultaneously crystallized with the primary MSS below ca. 850 °C and recrystallized into a low-form (low-temperature origin) Fe-rich pentlandite below ca. 600 °C. The primary MSS decomposed to Fe- and Ni-rich MSSs, low-form Ni-rich pentlandite, sugakiite, and heazlewoodite. The ISS decomposed to chalcopyrite below ca. 600 °C. Meanwhile, a Cu-Ir-Pt-Rh-thiospinel crystallized directly from the evolved Cu-rich sulfide melt below ca. 760 °C. Thus, Ir, Pt, and Rh preferentially partitioned into the melt phase during the crystallization process of the metasomatic sulfide melt. Metasomatic sulfide melts could be a significant medium for the transport and condensation of Pt together with Ir and Rh during the fractionation process in the Earth's interior. We hypothesize that the compositional variability of PGEs in carbonatites is due to the separation of sulfide melt leading to the loss of PGEs in the carbonatitic melts.

Ore mineralogy of the Rodu-Frasin Au-Ag deposit, Metaliferi Mountains, Romania

2020 ◽  
Author(s):  
Iatan Elena-Luisa
Keyword(s):  
Base Metal ◽  
Sedimentary Rocks ◽  
Metal Sulfides ◽  
Volcanic Structure ◽  
The North ◽  
Research And Innovation ◽  
Base Metal Sulfides ◽  
The Individual ◽  
Individual Grains ◽  
Low Sulfidation

<p>The Rodu-Frasin Neogene volcanic structure and associated Au-Ag mineralization are located in the north-eastern part of the Metaliferi Mountains, being part of the Baia de Aries - Rosia - Bucium metallogenetic district of the "Golden Quadrilateral".</p><p>The Rodu-Frasin region's geology consists mainly of Frasin dacite dyke and dome, polymictic volcanic and phreatomagmatic breccias and related volcano-sedimentary deposits, Badenian volcanic and sedimentary rocks, and Cretaceous sedimentary rocks.</p><p>Hydrothermal alteration in the region is pervasive and widespread throughout the volcanic structure and surrounding Cretaceous formation. Five main types of hydrothermal alterations have been described: potassic, propylitic, phyllic, silicic and carbonate. Argillic alteration is present only locally.</p><p>In the area of Rodu-Frasin deposit, the ore occurs in a structurally complex environment, influenced by faults and fractures oriented in two or more directions. Au-Ag-base metals mineralization is genetically associated with hydrothermal breccias and phreatomagmatic fractures.</p><p>Ore minerals consist of sulfides, gold, carbonates, adularia and quartz. They have been prevalently emplaced as veins, breccia bodies and disseminations in open fractures and breccias in the Rodu diatreme, and as stockworks, veins and disseminations in relationship to the Frasin dome structure.</p><p>The mineralized veins contain carbonates, quartz, pyrite, sphalerite, galena, chalcopyrite, tetrahedrite and gold. Magnetite and hematite, probably formed under mesothermal conditions, have been identified only as metasomatic substitutions of possible deep-breaking Cretaceous limestone clasts.</p><p>The deposition of the ore seemed to have a pulsating nature with the evolution taking place, possibly, in three stages to which the following mineral assemblages were described: 1. magnetite, hematite - pyrite, marcasite - quartz and pyrite - quartz ± base metal sulfides, in the first stage (mesothermal?); 2. arsenopyrite, Au - base metal sulfides - quartz - adularia, “chinga”, pyrite, Au - quartz - adularia and base metal sulfides - calcite, aragonite, dolomite, ankerite, ± rhodochrosite ± kutnahorite - quartz - adularia, in the second stage (epithermal low sulfidation) and 3. quartz - pyrite - marcasite - carbonates dominant rhodochrosite - Au and alabandite - rhodochrosite - quartz in the third stage (epithermal low sulfidation).</p><p>Gold is present in various proportions, either as small grains or as sub-microscopic occurrences and has been petrographically identified as electrum. The individual grains in native state have been observed as thin sheets on pyrite, sphalerite, rhodochrosite, calcite and quartz or as short wires and sheets in geodes. Local gold concentrations are common at the intersection of the locally-called “chairs” with “crosses” veins.</p><p><strong>Acknowledgments</strong></p><p>This work was supported by two Romanian Ministry of Research and Innovation grants, CCCDI – UEFISCDI, project number PN-III-P4-ID-PCCF-2016-4-0014 and PN-III-P1-1.2-PCCDI-2017-0346/29, within PNCDI III.</p>

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