Trace Elements in Sphalerite from the Dadongla Zn‐Pb Deposit, Western Hunan–Eastern Guizhou Zn‐Pb Metallogenic Belt, South China

Abstract

The western Hunan–eastern Guizhou Zn‐Pb metallogenic belt is one of the important Zn‐Pb mineralization regions in China. The Dadongla deposit, located in the northeast of Guizhou Province, is one of the typical Zn‐Pb deposits in the region and has estimated resources more than 12 million metric tons (Mt) with an average grade of 4.11 wt% Zn+Pb. Its orebodies are hosted in the lower Cambrian Aoxi Formation dolomite, occurring as bedded, para‐bedded in shape, and in conformity with the wall rock. The ore mineral assemblage is simple, dominated by sphalerite with minor pyrite and galena, and the gangue minerals are composed of dolomite, calcite with minor bitumen and barite. In view of the lack of geological and geochemical researches, the genesis of Zn‐Pb ore is still unclear. Laser ablation‐inductively coupled plasma mass spectrometry (LA‐ICPMS) spot and mapping analyses were used to obtain sphalerite trace element chemistry in the Dadongla Zn‐Pb deposit in Guizhou, China, aiming to constrain its ore genesis. The results show that sphalerite is characterized by the enrichment of Cd, Fe, Ge and Hg, corresponding with that of typical MVT deposits. Four zones were identified in the sphalerite crystal from Dadongla from the center to margin according to the color bands, in which the zone in the center, representing the early ore‐stage sphalerite, is characterized by enrichment of Cd relatively, while the zone forming at late ore‐stage is enriched in Ge and Hg relatively. The finding was controlled by differential leached metals content in ore‐forming fluid from its source rock. Notably, critical element Ge trends to be enriched at the late ore‐stage and follows a substitution of 2Zn2+↔ Ge4++□ (vacancy). Moreover, the calculated ore‐forming temperature ranges from 79.9°C to 177.6°C by the empirical formula, which is similar to that of typical Mississippi Valley‐type (MVT) deposits. Compared with the features of trace elements in sphalerite from different types of deposits, together with the geology, the Dadongla deposit belongs to an MVT Zn‐Pb deposit.

In situtrace elements and S isotope systematics for growth zoning in sphalerite from MVT deposits: A case study of Nayongzhi, South China

“…The colour-zoned sample shows a clear variation in both colour and S isotope composition from the core to rim (Figs 7−8 and 10). Although colour changes between some zones, especially within the CR texture of the sphalerite crystal do appear to correspond to an associated change in the S isotopic composition, this is not consistent, and the nature of the changes is not systematic between colour zones relative time (from crystal core to rim), which is in agreement with results from other studies (Belissont et al , 2014; Hu et al , 2020). This suggests that the change in sulfur isotopic compositions has no relationship with the colour-zoned sphalerite at Nayongzhi.…”

“…These elements also show a remarkable correlation with sphalerite colour. However, other studies of zoned sphalerite did not find a correlation between In, Sn, As and Ge and colour (Belissont et al , 2014; Hu et al , 2020). Therefore, the relationship between sphalerite and content of Pb, Ge, Tl, Mn Sb, Cd, Ga and Sn remains poorly constrained.…”

“…This trend suggests sphalerite with higher Fe concentration tends to be darker. In vein-hosted colour-zoned sphalerite of the Dadongla Zn–Hg deposit, South China, elevated Fe concentrations also correlate with brown sphalerite (Hu et al , 2020). Iron has the highest measured concentration in sphalerite compared to any other elements analysed in this investigation and a well-defined correlation between Fe concentration and sphalerite colour was identified.…”

“…Many studies have proposed two main mechanisms responsible for compositional zoning: (1) internal crystal growth processes representing self-organised phenomena controlled by kinetic factors, such as crystal growth rate and diffusion rate of key elements in the hydrothermal fluid (Fowler and L'Heureux, 1996; Holten et al , 1997; L'Heureux et al , 2000; Benedetto et al , 2005, Belissont et al , 2014); and (2) cyclic variations of external factors (e.g. temperature, , pH and mineralising fluid composition; Holten et al ,1997; Beaudoin, 2000; Kelley et al , 2004; Barrie et al , 2009; Pfaff et al , 2011; Gagnevin et al , 2012 and Hu et al , 2020).…”

“…pH, temperature and ), mineralising fluid composition and the S isotope variations are probably important (e.g. Kelley et al , 2004; Barrie et al , 2009; Pfaff et al , 2011; Hu et al , 2020 and reference therein).…”