Nonsulfide Ores Research Articles

Geochemistry, mineralogy, and development constraints of the Changarzeh non-sulfide ore, southern Natanz: Implications on tracing of carbonate rock-hosted supergene Pb-Zn deposits

Geochemistry, mineralogy, and development constraints of the Changarzeh non-sulfide ore, southern Natanz: Implications on tracing of carbonate rock-hosted supergene Pb-Zn deposits

Genesis of the Giant Huoshaoyun Non-Sulfide Zinc–Lead Deposit in Karakoram, Xinjiang: Constraints from Mineralogy and Trace Element Geochemistry

The Huoshaoyun zinc–lead deposit, a giant non-sulfide deposit in Xinjiang, is one of the most significant discoveries of zinc–lead deposit in China and globally in recent years. The deposit is dominated by zinc–lead non-sulfides, with minor occurrences of sulfides such as sphalerite, galena, and pyrite. The non-sulfide minerals include smithsonite, cerussite, anglesite, and Fe-oxide. This study focuses on the mineralogical characteristics of sulfide and non-sulfide ores, as well as the trace element characteristics of sphalerite, smithsonite, and Fe-oxide. Mineralogical analysis reveals that smithsonite is derived from the oxidation of primary sulfide minerals and can be classified into three types that are generated during different stages of supergene oxidation. The three types of smithsonite are formed through replacing the sphalerite and host limestone, as well as directly precipitating in the fissures and vugs. Trace element analysis of sphalerite indicates that it is rich in Cd, Tl, and Ge, but poor in Fe and Mn. The ore-forming temperature, calculated using the GGIMFis geothermometer, is mostly within the range of 100~150 °C. Moreover, the trace element characteristics, ore-forming temperature, and S and Pb isotope compositions of the sulfide ores of the Huoshaoyun deposit are similar to those of the Jinding and Duocaima MVT lead–zinc deposits, which are also located in the Eastern Tethyan zinc–lead belt. This suggests that the sulfide orebody in the Huoshaoyun Zn-Pb deposit could also be the MVT deposit. Study of the trace element of the non-sulfide minerals shows that the Mn and Cd are relatively enriched in smithsonite, while Ga, Ge, and Pb are enriched in Fe-oxide. This can be attributed to distinct geochemical properties of the trace elements in the non-sulfide minerals of the Huoshaoyun deposit and is consistent with those of the other oxidized MVT deposits, thus indicating the supergene oxidation process of this deposit.

On the impact of grinding conditions in the flotation of semi-soluble salt-type mineral-containing ores driven by surface or particle geometry effects?

Grinding and flotation processes are often studied independently, despite the well-established grinding influence on flotation performance, which affects not only particle size and thus liberation but also shape and leads to complex changes in pulp chemistry affecting the particle surface properties relevant for selective bubble attachment. Yet, no study jointly investigated these possible causes and many are limited to single mineral flotation. We relate grinding conditions to changes in pulp chemistry and particle surface properties and assess their impact on upgrading. We studied three non-sulfide ores with different feed grades and valuables: scheelite, apatite, and fluorite. These were dry-, wet-, and wet conditioned-ground before flotation in a laboratory mechanical cell. Results were evaluated with bulk- and particle-specific methodologies. The selectivity of the process is higher after dry grinding for the fluorite and apatite ores and irrelevant for the scheelite ore. Variations in flotation kinetics of individual particles associated to their size and shape are not sufficient to explain these results. The higher concentration of Ca2+ and Mg2+ observed in the pulp after wet grinding, altering particle surface properties, better explains the phenomenon. Additionally, we demonstrate how particle shape impacts are system specific and related to both entrainment and true flotation.

Analysis of the Application of Reagent Combination in the Flotation of Non-sulfide Ore

A brief review of articles on the flotation of minerals using a combination of reagents is presented. It is noted that the main attention of the authors is aimed at studying the effect of the combination of collectors at the mineral-liquid interface. It was shown that one of the reagents or associates formed as a result of their joint action, possessing surface activity, can serve as a desorbed form of sorption and help reduce the induction time during the formation of a flotation complex.

Microstructure, Mineralogical Characterization and the Metallurgical Process Reconstruction of the Zinc Calcine Relics from the Zinc Smelting Site (Qing Dynasty)

The smelting of zinc is considered as one of the most challenging technologies in ancient civilization. Compared with non-sulfide zinc ores, the smelting of zinc sulfide ores is more complicated since they have to be roasted before smelting. The technological smelting process of the ancient zinc metallurgy technology has been studied and partly reconstructed. However, the roasting technology, including the roasting conditions and involved metallurgical processes, is still unclear. The discovery of the zinc smelting site of Doulingxia dates back to the Qing dynasty (CE 1636–1912), and for the first time provides us with critical archeological evidence to gain an insight into the roasting technology in ancient zinc metallurgy technology. In this paper, the microstructure and mineralogical features of the zinc calcine relics found at the Doulingxia site were characterized by X-ray diffraction (XRD) and scanning electron microscopy coupled with X-ray energy dispersive spectrometer (SEM-EDS). To reconstruct the metallurgical process, the original roasting temperature of the unearthed zinc calcine was estimated by thermogravimetric analysis and differential thermal analysis (TG-DTA), combined with reheating experiments and phase composition analysis as well as microstructural analysis. The simulation experiments were conducted to reconstruct the roasting process. The results indicated that the original roasting temperature of the unearthed zinc calcine should be in a range of 650–850 °C, most probably near 750 °C. As long as the retention time is long enough, all sphalerite can be oxidized when the roasting temperature is above 650 °C. The final roasting products mainly include tiny porous particles of ZnFe2O4, Fe2O3, PbSO4, and ZnO. These findings are helpful to reconstruct the ancient zinc metallurgy technology of zinc sulfide ores.

Supergene nonsulfide Zn–Pb mineralization in the Mehdiabad world-class sub-seafloor replacement SEDEX-type deposit, Iran

The world-class Mehdiabad nonsulfide deposit consists of several accumulations of Zn–Pb–Fe nonsulfide minerals, derived from supergene of a vent-proximal sub-seafloor replacement SEDEX-type deposit hosted in lower Cretaceous clastic–carbonate rocks of the Taft and Abkuh Formations. The main sulfides are galena, sphalerite, pyrite, and minor amounts of chalcopyrite, which have been partially or completely transformed into nonsulfide minerals by supergene processes. Currently, the Zn mineralization in the Abkuh Formation (ore horizon II) is almost fully oxidized: the Mehdiabad deposit which can be assigned to both direct replacement and wall-rock replacement types. The time of the formation of the nonsulfide deposit has not been determined, but it is probable that the main supergene metallogenesis happened during Tertiary, possibly between post-Cretaceous to present. The mineralogy of the nonsulfide mineralization is generally complex and consists of smithsonite, hydrozincite, and hemimorphite as the main economic minerals, accompanied by cerussite, anglesite, iron–manganese oxy-hydroxides, sauconite, and Zn-rich clays. Commonly, nonsulfide minerals in this deposit consist of two types of ore: red zinc ore (RZO), rich in Zn, Fe, Pb-(As), and white zinc ore (WZO), typically with very high zinc grades but low concentrations of iron and lead. The proposed three-step scenario for the deposition of nonsulfide mineralization in the Mehdiabad deposit comprises: (1) the deposition of primary sulfides contemporaneous with lower Cretaceous clastic–carbonate host rocks to form SEDEX-type mineralization; (2) during the Late Cretaceous to present, regional uplift leads to deformation, folding, and thrusting of sulfide-bearing lower Cretaceous sequence; and (3) as a result, Zn–Pb–Fe sulfides hosted in carbonates experienced oxidation under an arid-warm climate to form the supergene nonsulfide ore mineralizations.

Geological, geochemical and microthermometric characteristics of the Hakkari region Zn-Pb deposits, SE Turkey

The Hakkari region in SE Turkey contains large Zn-Pb deposits, primarily of non-sulfide ore in Upper Triassic passive margin carbonates. In the Karakaya, Meskantepe and Üzümcü Zn-Pb deposit, the 3 main and >15 ore layers alternate with a thick-bedded limestone. The feeder in the region veins are well defined, containing both non-sulfide and sulfide ore. Primary sulfide ore contains between 1 and 37 % Zn, has transformed to “non-sulfide” ore containing Zn > 10%. Both non-sulfide and sulfide ore is associated with As, Se, Hg, Tl, Mn and Sb, which is similar to other SEDEX deposits. The average δ34S of the stratiform and feeder zone sulfides are 2.1‰ and 1.67‰, respectively. Sulfur isotope data of sphalerite, galena and pyrite (from −3.4 to 8.8‰) indicates that sulfur came from a homogeneous large source. Sulfate was reduced by the process of thermochemical sulfate reduction (TSR) rather than bacterial sulfate reduction (BSR). Lead isotope values (206Pb/204Pb ≈ 18.49, 207Pb/204Pb ≈ 15.66 and 208Pb/204Pb ≈ 38.69) reflect an evolved upper crustal source. The homogenisation temperature (Th) and salinity of fluid inclusions is from 165 to 289 °C, and from 1 to 22% equiv. NaCl salinity. Such a wide range of Th and salinity, and Cl/Br ratio (409 from sphalerite and galena; 662 from barite) of fluid inclusions may indicate mixing of basinal brines and seawater.Successive ore levels, laminated with shale-carbonate rich in organic matter, formed on the seafloor as banded and replacement ore. Trace element associations, fluid inclusion and isotope data indicate that the Zn-Pb deposits were formed as synsedimentary processes associated with feeder systems during the initiation of the Triassic rifting as a vent-proximal SEDEX-type. The metals (Pb, Zn, Fe) were leached from Palaeozoic and older clastic rocks in the Arabian platform by seawater sourced fluids, and ascended through deep fractures. The metalliferous fluids should have formed vein type mineralization in feeder zone, sub-seafloor replacement type ore under the ocean floor, and stratiform ore on the seafloor.

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

In supergene Zn non-sulfide deposits, the Fe-oxy-hydroxides (FeO/OH) are mainly concentrated in the residual zones (gossan) on top of the oxidized ore bodies, although they can also be found throughout the whole weathering profile coexisting with the primary and secondary ore assemblages. Fe-oxy-hydroxides are rarely pure as they form in systems where a wide range of metals, most of them of economic importance (e.g., Zn, Pb, Co, REE, Sc, Ga, Ge, V, etc.), freely circulate and can be “captured” under specific conditions. Although their occurrence can be widespread, and they have a potential to scavenge and accumulate critical metals, FeO/OH are considered gangue phases during the existing processing routes of Zn non-sulfide ores. Moreover, very little is known about the role of the deposit type on the geochemistry of FeO/OH formed in a specific association. Therefore, this paper provides a comprehensive assessment of the trace element footprint of FeO/OH from a number of Zn non-sulfide deposits, in order to define parameters controlling the metals’ enrichment process in the mineral phase. To achieve this, we selected FeO/OH-bearing mineralized samples from four supergene Zn non-sulfide ores in diverse settings, namely Hakkari (Turkey), Jabali (Yemen), Cristal (Peru) and Kabwe (Zambia). The petrography of FeO/OH was investigated by means of scanning electron microscope energy dispersive analysis (SEM-EDS), while the trace element composition was assessed using laser ablation-ICP-MS (LA-ICP-MS). Statistical analyses performed on LA-ICP-MS data defined several interelement associations, which can be ascribed to the different nature of the studied deposits, the dominant ore-formation process and subsequent evolution of the deposits and the environmental conditions under which FeO/OH phases were formed. Based on our results, the main new inferences are: (A) Zinc, Si, Pb, Ga and Ge enrichment in FeO/OH is favored in ores where the direct replacement of sulfides is the dominant process and/or where the pyrite is abundant (e.g., Cristal and Hakkari). (B) When the dissolution of the host-rock is a key process during the supergene ore formation (i.e., Jabali), the buffering toward basic pH of the solutions favors the uptake in FeO/OH of elements leached from the host carbonate rock (i.e., Mn), whilst restricting the uptake of elements derived from the dissolution of sulfides (i.e., Zn, Pb, Ga and Ge), as well as silica. (C) The input of exotic phases can produce significant enrichment in “unconventional” metals in FeO/OH (i.e., Cr and Co at Kabwe; Y at Cristal) depending on whether the optimal pH-Eh conditions are attained. (D) In the Kabwe deposit, FeO/OH records heterogeneous geochemical conditions within the system: where locally basic conditions prevailed during the alteration process, the V and U concentration in FeO/OH is favored; yet conversely, more acidic weathering produced Zn- and Si-bearing FeO/OH.

From Alpine-type sulfides to nonsulfides in the Gorno Zn project (Bergamo, Italy)

Recent exploration of the Gorno Zn-Pb-Ag deposit in northern Italy identified 3.3 Mt of sulfides at 4.9% Zn, 1.3% Pb, and 27.2 g/t Ag (indicated+inferred resources), and a further mineralized nucleus of mixed sulfides-nonsulfides in the Val Vedra area, currently under evaluation. The ores are hosted in Triassic limestone and shale. Sulfides (sphalerite, Ag-bearing galena, minor pyrite, and chalcopyrite) paragenetically follow Mn-Fe-bearing saddle dolomite and sparry calcite. The mineral association, and the carbon and oxygen isotope ratios of the sparry calcite (avg. δ13C = 1.0 ± 0.6‰ V-PDB; avg. δ18O = 19.63 ± 1.25‰ V-SMOW), are in agreement with precipitation from hydrothermal fluids in a deep burial setting. Sulfide emplacement occurred before the Alpine orogeny, likely during the Early-Middle Jurassic, in analogy to other Alpine-type deposits. The nonsulfide ore formed at the expense of sulfides, and mainly consists of smithsonite, hydrozincite, hemimorphite, and cerussite. The C-O-isotope values of the early generations of Zn-carbonates are characterized by δ18O between 24.1 and 26.8‰ V-SMOW and δ13C ratios between − 3.1 and 1.7‰ V-PDB. The later generations have lower δ18O (21.9 to 23.9‰) and lower δ13C (− 6.2 to − 3.9‰). These compositions, as those measured on cerussite (δ13C = −6.3 and − 7.7‰; δ18O = 14.0 and 15.3‰), agree with the formation of the nonsulfides in a supergene environment, under climatic conditions warmer than today. The δ18O decrease from early to late generations suggests progressive involvement of meteoric water sourced from higher altitudes. These characteristics indicate that the nonsulfides formed during the exhumation of the Gorno area from Miocene to Pliocene.

Major and trace elements and sulfur isotopes in two stages of sphalerite from the world-class Angouran Zn–Pb deposit, Iran: Implications for mineralization conditions and type

The Angouran deposit is the second-largest Zn–Pb deposit in Iran with 4.7 Mt sulfide ore (27.7% Zn, 2.4% Pb, and 110 g/t Ag) and 14.6 Mt nonsulfide ore (28.1% Zn, 4.4% Pb). Various models have been proposed to explain the genesis of sulfide ore in this deposit. Moreover, the mineralization type of its primary sulfide ores remains controversial. The major and trace element concentrations and sulfur isotopic composition of the two stages of sphalerite have been analyzed to constrain mineralization conditions and the genesis. The Angouran deposit, which contains discordant orebodies, is hosted in a Neoproterozoic/Cambrian schist-marble sequence. Two stages of sphalerite have been distinguished: early-stage (S1) red-brown sphalerite and late-stage (S2) honey-yellow sphalerite. Our result shows that, relative to the S2 sphalerite, the S1 sphalerite has higher contents of Fe, Mn, Co, Cu, Ag, Sn, Ga, Sb and In, but lower contents of As and Tl. Time-resolved depth profiles in these sphalerites determined by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses indicate that Fe, Cd, Co, Hg, Mn, Ge, and In are mainly present in solid solution and that Ag, Cu, Pb, As, Ni, Ga, Tl, Sb, and Sn are present in both solid solution and mineral inclusions. Correlation analyses reveal the occurrence of direct substitution mechanisms, such as Zn2+ ↔ (Fe2+, Cd2+) and 2Zn2+ ↔ Ge4++□ (vacancy) as well as coupled substitutions, such as 2Zn2+ ↔ Cu+ + Ga3+, 2Zn2+ ↔ (Cu+, Ag+) + Sb3+, 3Zn2+ ↔ Pb2+ + Tl+ + As3+, 4Zn2+ ↔ Pb2+ + 2As3++□(vacancy) or (Zn2+, Pb2+) ↔ Tl+ + As3+, and 4Zn2+ ↔ Cu+ + (Ga3+, In3+) + Sn4++□(vacancy). Geothermometer studies suggest that sphalerite in the Angouran deposit precipitated from a low-temperature (<200 °C) hydrothermal system. Trace element concentrations also reveal that the estimated average temperature of ore-forming fluid decreases gradually and becomes relatively oxidized from early stage to late stage. The low contents of Mn, and In and Zn/Cd ratios and high contents of Cd and Ge in sphalerite are consistent with those of MVT deposits but are different than that of magmatism-related deposits (e.g., epithermal, skarn, carbonate-replacement, and volcanogenic massive sulfide deposits). Meanwhile, the δ34SV-CDT values of the S1 and S2 sphalerites, which range from 5.1‰ to 10.9‰, are atypical of magma-derived sulfur isotopic compositions. Therefore, the Angouran deposit was formed in a low-temperature (<200 °C) fluid system and can be classified as a Mississippi Valley-type (MVT) deposit.

Metals Extraction from Sulfide Ores with Microorganisms: The Bioleaching Technology and Recent Developments

Nowadays, due to fast global industrial progress and near diminution of high-grade ore reserves, there has been massive call to cost-effectively process the resources of low-grade ores and industrial effluents for metal extraction. However, conventional approaches cannot be used to process such resources due to high capital cost and energy, also causing environmental pollution. Alternatively, bioleaching is highly environmental friendly and economic method to process such resources. Metal recovery from metal sulfide ore is carried out by chemolithotrophic bacteria like Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans. The same is done by heterotrophic microorganisms in non-sulfide ores. Additionally, for gold and copper extractions, bioleaching is used to extract cobalt, zinc, nickel, and uranium from low-grade ores and industrial effluents. In this review, the fundamental process of bioleaching from low-grade metal sulfide ores are discussed with emphasis on mechanism, types, pathways, techniques, and bioleaching development.

A global assessment of Zn isotope fractionation in secondary Zn minerals from sulfide and non-sulfide ore deposits and model for fractionation control

We investigated extent and direction of Zn isotope fractionation in secondary zinc minerals formed during low temperature hydrothermal and/or supergene oxidation of primary sulfide deposits. Zinc isotope data have been obtained from non-sulfide zinc mineral separates (willemite - Zn2SiO4, smithsonite - ZnCO3, hemimorphite - Zn4(Si2O7)(OH)2·H2O, hydrozincite - Zn5(CO3)2(OH)6, and sauconite - Na0.3Zn3(Si,Al)4O10(OH)2·4H2O) collected from several Zn deposits in Ireland, Belgium, Poland, Namibia, Peru, Yemen and Zambia. The data are compared with Zn isotope compositions measured on Zn sulfides collected in the same areas and/or derived from the existing literature, to establish the controls of direction and likely extent of any fractionations. We find that willemite has the greatest compositional variability, with measured δ66ZnJCM-Lyon values ranging from −0.42 to 1.39‰, spanning the entire range of terrestrial variation in Zn isotopes recorded to date. Overall, significant fractionations in positive and negative directions are recorded relative to the precursor phase (primary sphalerite or an earlier secondary phase), with primary sphalerite falling in a relatively narrow range of isotopic values (approximately −0.1 to +0.4‰). Most of the data observed on willemite, hemimorphite and hydrozincite can be explained with a model of isotopic fractionation, in which partial dissolution of primary sphalerite is followed by precipitation of an initial secondary phase that preferentially incorporates heavy Zn isotopes. Smithsonite, instead, preferentially incorporates light Zn isotopes. This reflects the variation in the Zn-x bond strengths of these secondary phases with respect to the original sulfides. We also observed that isotope compositions do not depend only on the difference between the fractionation factors of the involved phases but also on the amount of the secondary mineral precipitated after dissolution of primary sulfide, and that the greatest fractionations occur when only small amounts of secondary mineral are precipitated. Progressive precipitation from migrating fluids that form phases enriched in heavy zinc isotopes would lead to a gradual decrease in the δ66Zn values of such phases, and the fluids involved, in time and space. Strong negative isotopic shifts are almost only observed for late crystallizing phases, such as those in vugs. These are interpreted to reflect precipitation from residual, isotopically-light fluids that are the inevitable highly-fractionated product of the above-described process. Where a more complete replacement of primary sulfide has occurred, such as in the high-grade core of non-sulfide zinc orebodies, there is limited net isotopic fractionation because dissolved primary zinc is nearly quantitatively reprecipitated locally. In addition, in only one case (Yanque, Peru) we observed that the fringes of non-sulfide zinc deposit were characterized by isotopically fractionated compositions, with highly negative values implying extensive precipitation (earlier, or elsewhere) of isotopically heavy secondary phases. The higher-grade ore zones, where complete breakdown of primary sulfides and quantitative reprecipitation of zinc have occurred, show instead less fractionated compositions.

The Zn-Pb sulfide and Pb-Zn-Ag non-sulfide Kuh-e-Surmeh ore deposit, Zagros Belt, Iran: Geologic, mineralogical, geochemical, and S isotopic constraints

The carbonate-hosted Kuh-e-Surmeh deposit is located in the Zagros Simply Folded Belt, southwestern Iran. The semi-conformable tabular–like ore body lies within the northern flank of the NW–trending Kuh-e-Surmeh anticline. It is comprised of sulfide and non-sulfide base-metal ore types. The sulfide ore has a simple mineralogy and consists almost entirely of sphalerite, galena, and pyrite. Sphalerite is the main sulfide mineral having both crystalline and colloform texture. The Fe content of the sphalerite ranges between 0.04 and 8.9 wt% with the dark sphalerite zones containing higher (3.37–8.9 wt%) Fe values. Crystalline sphalerite is the main source of Ag in the sulfide ore. Galena formed simultaneously with and after sphalerite mineralization. The precipitation of pyrite occurred during the pre- to late sulfide ore mineralization phases. Anglesite is the most abundant non-sulfide mineral. Gray-colored, massive anglesite contains >100 ppm Ag, representing the main host of Ag mobilized during supergene events. On the basis geochemical data, in non-sulfide portion, there is an increase in Ag values with increasing Pb contents, independent of depth.The sulfur isotope enrichment factor (εSO4–primary sulfide minerals = 7.8‰) reflects the SO4−2 of the late stage gypsum formed by sulfate generated from the dissolution of primary sulfate minerals that mixed with sulfate originating from the oxidation and dissolution of sulfide minerals. Topographic relief, tectonic fracture systems, reactivation of the Surmeh Fault, and uplift related to the Zagros Orogeny all favored the establishment of arid climate conditions, providing an ideal environment for converting Zn-Pb sulfide ore to Pb-Zn-Ag non-sulfide ore.

Critical elements in non-sulfide Zn deposits: a reanalysis of the Kabwe Zn-Pb ores (central Zambia)

ABSTRACTThe Kabwe Zn-Pb deposit (central Zambia) consists of a cluster of mixed sulfide and non-sulfide orebodies. The sulfide ores comprise sphalerite, galena, pyrite, chalcopyrite and accessory Ge-sulfides (±Ga and In). The non-sulfide ores comprise: (1) willemite-dominated zones encasing massive sulfide orebodies and (2) oxide-dominated alteration bands, overlying both the sulfide and Zn-silicate orebodies. This study focuses on the Ge, In and Ga distribution in the non-sulfide mineralization, and was carried out on a suite of Kabwe specimens, housed in the Natural History Museum Ore Collection (London). Petrography confirmed that the original sulfides were overprinted by at least two contrasting oxidation stages dominated by the formation of willemite (W1 and W2), and a further event characterized by weathering-related processes. Oxygen isotopic analyses have shown that W1 and W2 are unrelated genetically and furthermore not related to supergene Zn-Pb-carbonates in the oxide-dominated assemblage. The δ18O composition of 13.9–15.7‰ V-SMOW strongly supports a hydrothermal origin for W1. The δ18O composition of W2 (−3.5‰ to 0‰ V-SMOW) indicates that it precipitated from groundwaters of meteoric origin in either a supergene or a low-T hydrothermal environment. Gallium and Ge show a diversity of distribution among the range of Zn-bearing minerals. Gallium has been detected at the ppm level in W1, sphalerite, goethite and hematite. Germanium occurs at ppm levels in W1 and W2, and in scarcely detectable amounts in hemimorphite, goethite and hematite. Indium has low concentrations in goethite and hematite. These different deportments among the various phases are probably due to the different initial Ga, In and Ge abundances in the mineralization, to the different solubilities of the three elements at different temperatures and pH values, and finally to their variable affinities with the various minerals formed.

C–O Stable Isotopes Geochemistry of Tunisian Nonsulfide Zinc Deposits: A First Look

A preliminary C–O stable isotopes geochemical characterization of several nonsulfide Zn-Pb Tunisian deposits has been carried out, in order to evidence the possible differences in their genesis. Nonsulfide ores were sampled from the following deposits: Ain Allegua, Jebel Ben Amara, Jebel Hallouf (Nappe Zone), Djebba, Bou Grine, Bou Jaber, Fedj el Adoum, Slata Fer (Diapir Zone), Jebel Ressas, Jebel Azreg, Mecella (North South Axis Zone), Jebel Trozza, Sekarna (Graben Zone). After mineralogical investigation of selected specimens, the C–O stable isotopic study was carried out on smithsonite, hydrozincite, cerussite and calcite. The data have shown that all the carbonate generations in the oxidized zones of Ain Allegua and Jebel Ben Amara (Nappe Zone), Bou Jaber, Bou Grine and Fedj el Adoum (Diapir Zone), Mecella and Jebel Azreg (North South Zone) have a supergene origin, whereas the carbonates sampled at Sekarna (Graben Zone) (and in limited part also at Bou Jaber) precipitated from thermal waters at moderately high temperature. Most weathering processes that controlled the supergene alteration of the Zn-Pb sulfide deposits in Tunisia had probably started in the middle to late Miocene interval and at the beginning of the Pliocene, both periods corresponding to two distinct tectonic pulses that produced the exhumation of sulfide ores, but the alteration and formation of oxidized minerals could have also continued through the Quaternary. The isotopic characteristics associated with the weathering processes in the sampled localities were controlled by the different locations of the sulfide protores within the tectonic and climatic zones of Tunisia during the late Tertiary and Quaternary.

Germanium enrichment in supergene settings: evidence from the Cristal nonsulfide Zn prospect, Bongar\xe1 district, northern Peru

Supergene nonsulfide ores form from the weathering of sulfide mineralization. Given the geochemical affinity of Ge to Si4+ and Fe3+, 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 (TGGIMFis) 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.

The Cristal Zn prospect (Amazonas region, Northern Peru). Part II: An example of supergene enrichments in tropical areas

The Cristal Zn prospect is located in the northernmost part of a wide mining district corresponding to the “Charlotte Bongará Zinc Project”, which covers an area of approximately 110 km2 in the Amazonas region in northern Peru. The mineralized area consists of many Zn occurrences that contain mixed sulfide and nonsulfide mineralizations. The nonsulfide ores are interpreted to be the product of weathering of primary MVT sulfide bodies. The Zn concentrations of the Cristal prospect are hosted by platform carbonates of the Condorsinga Formation (Early Jurassic), which belongs to the Pucará Group. The prospect extends over an area of approximately 2 × 1 km, with nearly continuous zones of Zn enrichment that has been detected in soil and rock samples. The nonsulfide mineralization consists mainly of semi-amorphous orange to brown zinc “oxides” that include hemimorphite, smithsonite and Fe-(hydr)oxides. The most important mineralized areas are the Esperanza and Yolanda occurrences, which were also most intensively explored. In both occurrences, the supergene Zn-carbonates and silicates infill solution cavities, or replace the carbonate host rocks and/or the primary sulfides, forming smithsonite- and hemimorphite-rich mineralizations. The analyzed drill core samples have on average 20 wt% Zn and maximum Ge concentrations of 200 ppm.The Bongará area experienced a prolonged phase of weathering from Miocene to Recent under tropical climatic conditions. In these conditions, the weathering processes affected many pre-existing sulfide deposits (e.g. Cristal, Florida Canyon, Mina Grande), where supergene profiles were developed under locally different settings that are defined primarily on the basis of mineralogical and geochemical data. Contrary to the Mina Grande deposit, at Cristal, the development of a karst network was minor due to limited uplift, and supergene alteration did not completely obliterate the roots of the original sulfide orebody. The mineralogy and geochemistry of Bongará nonsulfides is dependent on two main factors at the local scale: (1) uplift rates, and (2) host rock composition. The latter may have favored the development of more (e.g. Mina Grande) or less (e.g. Cristal) alkaline supergene environments. Uplift was controlled by the activity of local faults, which allowed the exposure of sulfide protores at variable elevations in different periods of time and hydrological settings. Such different settings resulted in the precipitation of isotopically different supergene carbonates (e.g. smithsonites and calcites at Mina Grande and Cristal).

Zn-clay minerals in the Skorpion Zn nonsulfide deposit (Namibia): Identification and genetic clues revealed by HRTEM and AEM study

Zn-clays worldwide occur in various supergene nonsulfide (Zn-Pb) ores, where they can be the prevailing economic minerals or represent minor concentrations in the mineral assemblage. The world-class Zn smectite-rich Skorpion mine (Namibia) is considered one of the most important supergene nonsulfide zinc deposits in the world. At Skorpion, the trioctahedral Zn-bearing smectite predominates over the other Zn-oxidized minerals. This work is focused on microtextural observation and chemical analyses on the clay nano-particles of the supergene nonsulfide ores from Skorpion, carried out for the first time using TEM/HRTEM and AEM investigations. This approach helped to better understand the formation mechanism of the Skorpion Zn-clays and related phases down to the nanoscale. The microtextures of the Skorpion Zn-clays suggest they formed from fluids, meteoric and/or hydrothermal in nature, in two textural contexts: smectites can grow on previously deposited phyllosilicates (mica) (CCP texture), and/or directly nucleate from Zn-rich solutions (PCA texture). The Skorpion sauconite is chemically characterized by a greater homogeneity if compared with natural sauconites from other occurrences; it is quite stoichiometric, with Ca as interlayer cation and limited quantities of Mg and Fe, with an average composition of Ca0.14K0.02(Zn2.7Mg0.09Al0.14Fe0.10)(Si3.4Al0.6)O10(OH)2·nH2O. Contrary to Peru nonsulfide ores (Accha and Yanque), at the micro- and nanoscale the occurrence of Zn-beidellite at Skorpion is very subordinated. Chlorite and baileychlore have been also detected. Detrital micas are commonly the template for epitaxial sauconite growth. Typical supergene processes at ambient temperatures should be considered for the genesis of the Skorpion sauconite-bearing deposit, with some local contribution of low-T hydrothermal fluids. The micro- and nano-features of the Skorpion mineral assemblage confirm the complex mineralogical nature of the smectite-rich nonsulfide (micro)systems, with remarkable implications for mineralogical evaluation and processing.

The Karst-Hosted Mina Grande Nonsulfide Zinc Deposit, Bongará District (Amazonas Region, Peru)

The Mina Grande zinc nonsulfide deposit (Amazonas region, Peru) consists of several accumulations in karst cavities of Zn oxide minerals, derived from weathering of a Mississippi Valley-type deposit hosted in Mesozoic carbonate rocks of the Condorsinga Formation (Pucara Group). The karst cavities hosting the nonsulfide ores were developed in the Miocene along northwest-southeast faults (avg 230° dip, 70° dip angle) associated with regional structures, and locally along stratification joints (avg 8° strike, 278° dip, and 26° dip angle). Thus far, the Mina Grande Zn accumulations have been partially mined in two pits (named “Fase A” and “Fase B”) and explored in a third area, named “Fase C.” In 2008, the resources were as follows: Fase A = 160,000 metric tons (t) @ 21.2% Zn, Fase B = 36,400 t @ 28.9% Zn, and Fase C = 116,700 t @ 22.5% Zn. The nonsulfide mineral assemblage, consisting mostly of hydrozincite, smithsonite, and hemimorphite, is associated with few remnants of the hypogene ore (pyrite and sphalerite). Mineralogical and petrographic studies revealed several texturally distinct smithsonite and hydrozincite generations, which are characterized by extremely negative δ 13 C compositions, pointing to the prevailing contribution of an isotopically light carbon component from the oxidation of organic matter-derived carbon, and different δ 18 O isotope compositions: 26.9 to 27.2 and 26.0 to 26.3‰ δ 18 O VSMOW for smithsonite, and averages 24.6 and 23.7‰ δ 18 O VSMOW for hydrozincite. These distinct δ 18 O compositions indicate that smithsonite and hydrozincite precipitated at least after two depositional stages. These stages were probably related to several periods of uplift that occurred in the Bongara district since at least ~10 Ma, when the transition from the Pebas to Acre systems affected the Amazonas foreland basin in the Miocene. The karst activity, to which the supergene mineralization is related, was restricted to the late Miocene and early Pliocene periods. Climatic conditions reconstructed from the ecosystems persisting in the region from Late Tertiary to Recent time suggest that the Mina Grande supergene mineralization was associated with several weathering episodes that occurred under a climate resembling the present-day climatic conditions.

Развитие и функционирование микроорганизмов в циклах обогащения сульфидных медно- никелевых и несульфидных апатит-нефелиновых руд

Развитие и функционирование микроорганизмов в циклах обогащения сульфидных медно- никелевых и несульфидных апатит-нефелиновых руд