Topic
Alloclasite
About: Alloclasite is a research topic. Over the lifetime, 4 publications have been published within this topic receiving 54 citations.
Papers
TL;DR: In this article, the mineral assemblages and chemical compositions of ore minerals from the Boroo gold deposit in the North Khentei gold belt of Mongolia were studied to characterize the gold mineralization, and to clarify crystallization processes of the ore minerals.
Abstract: Mineral assemblages and chemical compositions of ore minerals from the Boroo gold deposit in the North Khentei gold belt of Mongolia were studied to characterize the gold mineralization, and to clarify crystallization processes of the ore minerals. The gold deposit consists of low-grade disseminated and stockwork ores in granite, metasedimentary rocks and diorite dikes. Moderate to high-grade auriferous quartz vein ores are present in the above lithological units. The ore grades of the former range from about 1 to 3 g/t, and those of the latter from 5 to 10 g/t, or more than 10 g/t Au. The main sulfide minerals in the ores are pyrite and arsenopyrite, both of which are divisible into two different stages (pyrite-I and pyrite-II; arsenopyrite-I and arsenopyrite-II). Sphalerite, galena, chalcopyrite, and tetrahedrite are minor associated minerals, with trace amounts of bournonite, boulangerite, geerite, alloclasite, native gold, and electrum. The ore minerals in the both types of ores are variable in distribution, abundance and grain size. Four modes of gold occurrence are recognized: (i) “invisible” gold in pyrite and arsenopyrite in the disseminated and stockwork ores, and in auriferous quartz vein ores; (ii) microscopic native gold, 3 to 100 µm in diameter, that occurs as fine grains or as an interstitial phase in sulfides in the disseminated and stockwork ores, and in auriferous quartz vein ores; (iii) visible native gold, up to 1 cm in diameter, in the auriferous quartz vein ores; and (iv) electrum in the auriferous quartz vein ores. The gold mineralization of the disseminated and stockwork ores consists of four stages characterized by the mineral assemblages of: (i) pyrite-I + arsenopyrite-I; (ii) pyrite-II + arsenopyrite-II; (iii) sphalerite + galena + chalcopyrite + tetrahedrite + bournonite + boulangerite + alloclasite + native gold; and (iv) native gold. In the auriferous quartz vein ores, five mineralization stages are defined by the following mineral assemblages: (i) pyrite-I; (ii) pyrite-II + arsenopyrite; (iii) sphalerite + galena + chalcopyrite; (iv) Ag-rich tetrahedrite-tennantite + bournonite + geerite + native gold; and (v) electrum. The As–Au relations in pyrite-II and arsenopyrite suggest that gold detected as invisible gold is mostly attributed to Au+1 in those minerals. By applying the arsenopyrite geothermometer to arsenopyrite-II in the disseminated and stockwork ores, crystallization temperature and logfs2 are estimated to be 365 to 300 °C and –7.5 to –10.1, respectively.
11 citations
TL;DR: In this paper, three transitional paragentic stages of hypogene mineralization have been identified at Baycheh-Bagh mine in NW Iran, where the sulfarsenides and arsenides reveal significant substitution of Ni, Co, Fe and S reflecting compositional changes of the ore forming fluid (e.g., activities of metals, As/S) as well as changes in pH and oxidation state.
11 citations
TL;DR: The Black Butte copper deposits as discussed by the authors are a group of sediment hosted, laterally extensive Cu-Co-Ag deposits hosted in dolomitic shale of the mid-Proterozoic Newland Formation.
Abstract: The Black Butte copper deposits (formerly known as Sheep Creek) are a group of sediment hosted, laterally extensive Cu–(Co–Ag) deposits hosted in dolomitic shale of the mid-Proterozoic Newland Formation. Copper–cobalt mineralization occurs in zones of massive, laminated pyrite that were locally reworked and infiltrated by Cu-rich fluids during early diagenesis. Cobalt, along with substantial nickel and arsenic, mainly occurs as impurities within early, porous pyrite, or as minute grains of sulpharsenides (i.e., cobaltite, glaucodot, and/or alloclasite). Later thermal events remobilized the Co, Ni, and As to form intergrowths of siegenite (Co,Ni)3S4 and tennantite. The temperature of this later event is constrained by the mineralogical assemblage to have been relatively low, between 125 and 225 °C. Although many of the characteristics of SEDEX-type deposits are present at Black Butte (e.g., laterally extensive massive pyrite horizons, interbedded black shales, abundant barite and local phosphate horizons, and rifted continental margin setting), the lack of economic Pb and Zn mineralization in the main deposits, and the abundance of Cu with high Co, is more typical of sediment-hosted stratiform copper deposits. The Neihart Formation, a hematitic quartz sandstone resting below the base of the Belt Supergroup, may have been an important source bed for Cu–Co–Ni–Ag fluids. It is speculated that these fluids, ideal for forming Cu deposits, were expelled along growth faults near the margin of the Belt Basin and deposited metals on or just below the sea floor in a setting that is typical of SEDEX deposits. This unique mineral deposit model may have applications to other districts where Cu–Co-rich sulfides are deposited in an exhalative setting.
9 citations
TL;DR: In this paper, a pyrrhotite matrix was found as localized segregations in the Arroyo de la Cueva area, at the northwestern margin of the Ronda Peridotite.
Abstract: Fe–Co–Ni sulfarsenides and diarsenides in a pyrrhotite matrix were found as localized segregations in the Arroyo de la Cueva area, at the northwestern margin of the Ronda Peridotite. The pyrrhotite matrix encloses alloclasite, lollingite and pentlandit e, and is cross-cut by veins of chalcopyrite–cubanite intergrowths hosting arsenopyrite, cobaltite and sphalerite, as well as chlorite – magnetite and calcite–talc with minor arsenopyrite and lollingite. Alloclasite, arsenopyrite, cobaltite, lollingite and pentlan dite show strong variation in their contents of Fe, Co, Ni, As and S. Textural and chemical evidence suggests that the ore initially formed at high temperatures and low fugacities of sulfur. The ore was subsequently metasomatized at conditions of gradually increasing sulfur fugacity and decreasing temperatures. The variations in Fe, Co and Ni in alloclasite, cobaltite and pentlandi te describe linear trends. These trends were compared with similar trends from other, especially mafic–ultramafic associations. They depend on both mineral association and the requirement that a structure-specific number of nonbonding metal d electrons be maintained. Three types of trends are shown by the sulfarsenides. 1) Trends describing Co replacement by a mixture of Fe and Ni are shown by sulfarsenides occurring in metal-rich environments. 2) Trends where Co is replaced by Ni occur in associations containing either pyrite, sulfarsenides or diarsenides indicative of higher anion fugacities. 3) Trends shown by sulfarsenides associated with skutterudite describe replacement of Ni by a mixture of Co and Fe. The trends defined by pentlandite compositions indicate the substitution Fe + Ni → 2 Co and support previously suggested bonding models.
Related Topics (5)
Performance Metrics
| Year | Papers |
|---|---|
| 2020 | 1 |
| 2015 | 1 |
| 2014 | 1 |
| 2001 | 1 |