A New Zincian Greenockite Occurrence in the Saishitang Cu Skarn Deposit, Qinghai Province, Northwest China

Abstract

Zn-Cd-S series minerals not only comprise industrial resources for Zn and Cd, but are also significant mineralogical indicators for hydrothermal ore-forming processes. Due to its unique formation conditions and rare occurrence, our understanding of the formation of zincian greenockite in natural systems is limited. Zincian greenockite was discovered during mineralogical studies in the Saishitang Cu skarn deposit, Qinghai Province, Northwest China. This provided an ideal opportunity to assess the occurrence and formation of zincian greenockite in skarn-type deposits. Ore minerals were observed using reflected-light microscopy, and the zincian greenockite was further analyzed using electron-probe microanalysis (EPMA) and X-ray diffraction (XRD). The zincian greenockite occurs in the bornite-chalcopyrite ores and is composed of subhedral to anhedral grains approximately 50 × 150 µm 2 to 200 × 300 µm 2 in size, replaces the bornite, and is replaced by native silver. Two phases (I and II) were identified based on back-scattered electron images, X-ray element-distributions maps, and EPMA data. The textural relationship indicated that Phase I was replaced by Phase II. Phase I contained high Zn (14.6 to 21.7 mol % ZnS) and low Cd (72.4 to 82.2 mol % CdS), while Phase II contained low Zn (5.6 to 9.1 mol % ZnS) and high Cd (85.4 to 89.9 mol % CdS). The zincian greenockite was formed at temperature of 300~270 • C during the transformation from a reducing environment to an oxidizing one in the late stage of the mineralization process in the Saishitang deposit.

Genesis of greenockite (CdS) and associated sulphide‐gold mineralization from Mahakoshal belt, Central Indian Tectonic Zone

“…T A B L E 4 The temperature of ore formation inferred from the sphalerite specimen of Bagdha prospect, Mahakoshal belt, after geothermometer (GGIMF) was proposed (Frenzel et al, 2016). 6) from epithermal deposits (Marcoux et al, 1993;Tombros et al, 2005), hydrothermal (Mogessie et al, 2009;Oen et al, 1974;Tarkian & Breskovska, 1989), stratiform Pb-Zn-Ag deposits (Patterson, 1985), fumaroles (Chaplygin et al, 2007), Skarn Deposits (Liu & Zhang, 2017) and from the present study (Figures 4 and 6). Box plot (Figure 6b)…”

“…Rare greenockite is associated with orogenic gold deposits in western Australia (Golding, 1978). Greenockite occurrence was also reported in the Saishitang Cu Skarn Deposit, Qinghai Province, Northwest China, which was suggested to have formed during a change from reducing to oxidizing conditions (Liu & Zhang, 2017).…”

“…(b) Box plot showing the variation in Cd, Zn, S (wt%) of greenockite of present study compared with data on greenockite from the world literature. Source : Mogessie et al (2009), Mishra and Hazarika (2016), Liu & Zhang, 2017 and references therein.…”

“…Greenockite associated with sphalerite having varying concentrations of mol% ZnS and CdS, [Gck‐1 contain high Zn (10.81 to 26.94 mol% ZnS) and low Cd (70.76 to 87.48 mol% CdS), while Gck‐2 includes low Zn (2.96 to 12.541 mol% ZnS) and high Cd (87.22 to 98.29 mol% CdS)] respectively, has been reported (Table 6) from epithermal deposits (Marcoux et al, 1993; Tombros et al, 2005), hydrothermal (Mogessie et al, 2009; Oen et al, 1974; Tarkian & Breskovska, 1989), stratiform Pb–Zn–Ag deposits (Patterson, 1985), fumaroles (Chaplygin et al, 2007), Skarn Deposits (Liu & Zhang, 2017) and from the present study (Figures 4 and 6). Box plot (Figure 6b) shows uniform concentrations of Cd in all deposits except fumaroles type.…”

“…Greenockite is stable over various temperatures (250–1050°C) and Eh‐pH conditions (Kaneko et al, 1984; Kroger, 1939). It can have diverse origins and can be found in distinct geological environments, which include granites and pegmatites, fumaroles, various hydrothermal deposits, sediment‐hosted Pb‐Zn deposits (Mogessie et al, 2009 and references therein), orogenic gold deposits (Golding, 1978), chromite‐PGE deposits (Mishra & Hazarika, 2016), and skarn deposits (Liu & Zhang, 2017). Cadmium is an essential structural component in 27 minerals: 10 sulphides, 7 sulphates, 4 arsenates, 2 phosphates, and 1 oxide, selenite, and carbonate, plus native Cd (Yaciuk et al, 2022).…”