Germanium enrichment in supergene settings: evidence from the Cristal nonsulfide Zn prospect, Bongará district, northern Peru

Abstract

Supergene nonsulfide ores form from the weathering of sulfide mineralization. Given the geochemical affinity of Ge to Si 4+ and Fe 3+ , weathering of Ge-bearing sulfides could potentially lead to Ge enrichments in silicate and Fe-oxy-hydroxide minerals, although bulk rock Ge concentrations in supergene nonsulfide deposits are rarely reported. Here, we present the results of an investigation into Ge concentrations and deportment in the Cristal supergene Zn nonsulfide prospect (Bongará, northern Peru), which formed from the weathering of a preexisting Mississippi Valley-type (MVT) sulfide deposit. Material examined in this study originates from drillcore recovered from oxidized Zn-rich bodies~15-20 m thick, containing~5-45 wt% Zn and Ge concentrations~100 ppm. Microanalysis and laser ablation-ICP-MS show that precursor sphalerite is rich in both Fe (mean Fe = 8.19 wt%) and Ge (mean Ge = 142 ppm). Using the mineral geothermometer GGIMFis-geothermometer for Ga, Ge, In, Mn, and Fe in sphalerite-proposed by Frenzel et al. (Ore Geol Rev 76:52-78, 2016), sphalerite trace element data from the Cristal prospect suggest a possible formation temperature (T GGIMFis ) of 225 ± 50°C, anomalously high for a MVT deposit. Germanium concentrations measured in both goethite (mean values 100 to 229 ppm, max 511 ppm) and hemimorphite (mean values 39 to 137 ppm, max 258 ppm) are similar to concentrations measured in hypogene sphalerite. Additionally, the Ge concentrations recorded in bulk rock analyses of sphalerite-bearing and oxidized samples are also similar. A persistent warm-humid climate is interpreted for the region, resulting in the development of an oxidation zone favoring the formation of abundant Zn hydrosilicates and Fe hydroxides, both able to incorporate Ge in their crystal structure. In this scenario, Ge has been prevented from dispersion during the weathering of the Ge-bearing sulfide bodies and remains in the resultant nonsulfide ore.

Trace Element Contents in Sphalerite from the Nayongzhi Zn-Pb Deposit, Northwestern Guizhou, China: Insights into Incorporation Mechanisms, Metallogenic Temperature and Ore Genesis

“…The strong anti-correlation between Zn and Fe (R 2 = −0.96; Figure 9b) in our data support specific studies on trace element incorporation in sphalerite [6,8,51,52], which is suggestive of a direct substitution of divalent cations as Zn 2+ ↔Fe 2+ (Figure 8c). Moreover, Figure 10 shows that the strong negative correlation is observed among (Cd + In + Sn + Sb + Fe + Mn + Cu + Ga + Ge + Ag + Co) and Zn (R 2 = −0.94), which suggests that those trace elements (Cd, In, Sn, Sb, Fe, Mn, Cu, Ga, Ge, Ag and Co) mainly exist in the form of isomorphism in sphalerite that is thought to be involved in the mechanism of their enrichment in sphalerite [4,5,53,54].…”

“…Sphalerite (ZnS), one of the most common sulfide minerals, is the major ore of zinc, and approximately 95% of all primary zinc worldwide is extracted from sphalerite ores. Previous studies have shown that the crystal structure of sphalerite could incorporate a broad variety of elements, with the most significant being Fe, Cd, Ga, Ge and In [1][2][3][4][5][6][7][8], along with the presence of some other elements (e.g., Hg, Ag and Cu) [4][5][6][7][9][10][11]. Several studies have noted that substitution of Zn 2+ by bivalent similar-sized cations (e.g., Pb 2+ , Cd 2+ and Co 2+ ) or by coupled substitution mechanisms, which can be extended to tri-and tetravalent elements (e.g., Sb 3+ , In 3+ and Ge 4+ ).…”

“…Recently, Frenzel et al [7] offered a new sphalerite geothermometer (GGIMFis), which could be applied to calculate the ore-forming temperature of various deposit types, based on the assumption that Fe, Mn, Ga, Ge, and In are incorporated in the crystal lattice of sphalerite. This geothermometer firstly was used to calculate the ore-forming temperature of the Cristal nonsulfide Zn prospect, Bongará district, northern Peru by Mondillo et al [8]. Furthermore, it has been recognized relatively recently that the trace element endowment of sphalerite can, to a large extent, be correlated with genetic type [4][5][6]15,16].…”

Identification of Zn-Bearing Micas and Clays from the Cristal and Mina Grande Zinc Deposits (Bongará Province, Amazonas Region, Northern Peru)

“…The bulk mineralogy of the drillcore samples [35] is characterized by ubiquitous quartz and muscovite. The mineralogy of the sulfide bodies is relatively simple, and mostly consists of disseminated dark-brown and Fe-rich sphalerite [49,53], with lesser amounts of pyrite and galena. The nonsulfide mineral association is quite complex, being represented by a wide suite of supergene minerals: smithsonite, hemimorphite, hydrozincite, chalcophanite, goethite, and greenockite [35].…”

Influence of Genetic Processes on Geochemistry of Fe-oxy-hydroxides in Supergene Zn Non-Sulfide Deposits

“…A few research papers on the geochemistry of FeO/OH associated with supergene non-sulfide mineralization have been published by Mondillo et al [16][17][18][19][20], Santoro et al [21][22][23], Navarro-Ciurana et al [24], Arfè et al [25,26] and Stavinga et al [27]. In their studies, they report that the FeO/OH are commonly enriched in Zn and Pb with traces of several other elements, such as As, Cd, Co, Cu, Ga, Ge, Hg, In, Mo, Ni, Sb, Sc and V. This enrichment can depend on: (i) the chemistry of the primary deposit, and (ii) the pH, Eh and T properties of the fluids circulating during the formation of the deposit [28].…”