Inclusions Of Galena Research Articles

Atypical chromitite deposit in the Gaositai mafic-ultramafic complex, North China Craton: Geochemical, geochronological, and isotopic systematics

The Gaositai mafic-ultramafic complex in the North China Craton hosts a significant chromitite deposit featuring morphological and geochemical characteristics that deviate from the usual characteristics of typical high-Cr and low-Al podiform chromitites. Field observations and microscopic studies reveal notable variations in textural layering, mineralogy, and geochemical composition, challenging conventional features of stratiform chromitite deposits. Zircon UPb ages indicate that chromitite is most likely Carboniferous-Permian in age (330–275 Ma), but also contains numerous inherited zircons with concordant ages as old as 2544 Ma, reflecting a complex geological evolution. Post-formation metasomatic or metamorphic imprints can be evident by concordant zircon ∼247 Ma. Variable zircon εHf(t) values (−15 to +9.6) and depleted mantle model ages (432 to 2819 Ma) attest the presence of heterogeneous or reworked source materials.The PGE and trace element characteristics of the Gaositai chromitite are comparable to the geochemical features of Bushveld and Great Dyke deposits. Pyrite, millerite, norsethite, galena, and PGM (mainly OsIr alloys) inclusions are ubiquitous in chromite. Galena inclusions with homogenous Pb-isotopic ratios (206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb) suggest a mixed sources of lead. In contrast, pyrite inclusions display significant variations in δ34SV-CDT values (−0.11 ‰ to 18.31‰) indicative of a crustal origin of sulfur. Bulk-rock ReOs isotope data of 0.1264–0.1294 shows 187Os/188Os ratios similar to abyssal peridotites, implying a potential connection between chromitite and the host ultramafic rocks. Highly disparate mantle model ages (55 to 2141 Ma) and re-depletion ages (28 to 692 Ma) suggest disturbance of the ReOs isotopic system during post-formational metasomatic or metamorphic events. These variations may, alternatively, reflect heterogeneity by subduction components. The obtained results do not support the Alaskan-type genesis of the host complex, but point towards an atypical stratiform type.

The Mineral and Geochemical Features of Sulfides in the Jade Hydrothermal Field of the Okinawa Trough in Off-Shore China

In this study, mineralogical and elemental geochemical characteristics of massive sulfide samples collected from the Jade hydrothermal field, located in the Izena depression in the central graben of the Okinawa Trough, were analyzed by means of optical microscopy, scanning electron microscopy, and electron probe microanalysis (EPMA). The results show that the mineralization in the Jade hydrothermal field can be divided into Zn-Cu-Pb-rich massive sulfides and Zn-Fe-rich massive sulfides. The former is composed of sphalerite, galena, chalcopyrite, pyrite, and anglesite, which is the product of the low-temperature alteration of galena. The latter is mainly composed of sphalerite, pyrite, marcasite, and traces of galena. Cu and Zn in pyrite may exist in the form of microinclusions, while Ag and Pb may exist in pyrite in the form of fine galena inclusions containing Ag. Fe and Cu may enter sphalerite in the form of ion replacement. Zn may enter chalcopyrite in the form of ion replacement. Consistent with the previous understanding, the metal elements in the hydrothermal liquid system in the Jade hydrothermal field mostly migrated as sulfur complexes, and when the hydrothermal fluid mixes with seawater, the physical and chemical conditions of the fluid change, resulting in sulfide mineral precipitation. However, the chemical structure of chalcopyrite is still controversial, which restricts the understanding of the substitution mechanism of trace elements during chalcopyrite precipitation.

Fluid source and physicochemical conditions of the polymetallic mineralization in Gawuch Formation, Kohistan Island Arc, NW Pakistan

The Cu-Sb-Pb polymetallic vein deposit is hosted by metavolcanics rocks of the Gawuch Formation at the Kaldom Gol area of the northwest Kohistan arc terrain in northern Pakistan. The mineralization is closely associated with the dioritic to granodioritic rocks of the Lowari pluton, which was intruded into the Gawuch metavolcanics. Details of ore characterization and processes of ore genesis of this evidently hydrothermal mineralization are not well documented. Integrating petrographic, mineral-chemical and isotopic investigations, this study aims to comprehend the source of hydrothermal fluids, geochemical evolution, mineral inclusions and physicochemical conditions of the Cu-Sb-Pb polymetallic vein deposit in Gawuch metavolcanics in the Kohistan arc terrain in northern Pakistan. The mineralization is distinguished into three types of ore-gangue associations: Type Ia, Type Ib, and Type II. The textural study revealed two pyrite generations: (i) Py1 displaying euhedral to subhedral habits and containing scarce inclusions, and (ii) Py2 occurring as anhedral grains hosting abundant inclusions. Type Ia is characterized by Py1 associated with abundant quartz (Qz) showing comb texture, sericite (Ser), and minor chlorite (Chl). Type Ib comprises Qz + Ser + Chl and Py2, chalcopyrite (Ccp), and magnetite (Mag). Type II is represented by mosaic quartz, rhombic adularia, and bladed calcite, and the ore minerals fahlore and galena. Alteration zones composed of Qz-Ser ± Chl and Qz-Ser-Chl, surround Type I (a, b) and Type II veins, respectively. Fahlore and galena mostly replace pyrite of Type Ia and chalcopyrite of Type Ib. In addition, malachite, azurite, hematite and covellite occur as secondary (supergene) minerals. The Co/Ni ratios (>1) of Kaldom Gol pyrites suggest that the ore-forming fluids were hydrothermal in origin and Py1 and Py2 solidified at 221–304 °C and 225–261 °C, respectively. The LA-ICP-MS time-resolved depth profiles confirm the existence of sphalerite, and chalcopyrite inclusions in pyrite (Py1 and Py2) and millerite, bravoite, vaesite, Au-tellurides, native Au and galena inclusions in chalcopyrite and fahlore. Sulfur isotope compositions of pyrites (δ34S = Py1, −0.58 to +2 ‰; δ34S = Py2, −0.24 to +2.04 ‰) indicate that the ore-forming fluids were derived from magmatic source (s). The mineral assemblage, hydrothermal alterations, textures, temperature and δ34S of pyrites suggest that the Cu-Sb-Pb polymetallic mineralization at Kaldom Gol represents an intermediate-sulfidation type of epithermal deposit.

Resetting of the U-Pb and Th-Pb systems in altered bastnäsite: Insight from the behavior of Pb at nanoscale

AbstractBastnäsite contains considerable amounts of U and Th and has been widely used for U-Th-Pb dating. Hydrothermal alteration of bastnäsite is common in nature but its effects on U-Th-Pb dating are not currently well constrained. Hence the significance of U-Th-Pb ages obtained from altered bastnäsite cannot be evaluated. Here, we present a detailed geochronologic as well as micro- and nano-scale mineralogical study of altered bastnäsite in a Mo-REE deposit, Central China. The original bastnäsite grains were confirmed to have crystalized at 208 Ma but were variably overprinted by a hydrothermal event at 150 Ma. They commonly exhibit typical replacement textures that appear to have formed from a coupled dissolution-reprecipitation process, i.e., a primary unaltered domain surrounded by a porous altered domain. Micro- and nano-scale mineralogical observations strongly suggest that during the coupled dissolution-reprecipitation process, non-radiogenic (common) Pb was incorporated into the altered domains in the form of nanoscale galena inclusions. Such incorporation (even minor) has significantly affected the 206Pb/238U and 207Pb/206Pb ratios due to the low contents of U and its daughter isotopes in bastnäsite, resulting in highly variable, discordant U-Pb dates for the altered domains. In contrast, incorporation of the non-radiogenic Pb has very limited effects (<5%) on the Th-Pb system due to the remarkably high contents of Th and radiogenic 208Pb in bastnäsite. Instead, the scattered 208Pb/232Th ages (208 to 150 Ma) of the altered domains were essentially affected by incomplete replacement, and thus can be used to approximate the lower age limit of the primary hydrothermal activity or the upper age limit of the secondary hydrothermal activity. The results from this study highlight that because of the different orders of magnitude between the U and Th contents in bastnäsite, the mobilization of radiogenic and non-radiogenic Pb during alteration may have significantly different impacts on the U-Pb and Th-Pb systems. Therefore, the two systems should be treated separately during the dating of bastnäsite resulting from secondary hydrothermal events.

AGE AND DURATION OF CRYSTALS GROWTH IN CHAMBERS OF VOLYN PEGMATITES (UKRAINIAN SHIELD)

Formation of chamber pegmatites is associated with tectonomagmatic activation of the region of their distribution. It should be expected that the granitic chamber pegmatites of Volyn were formed by products of degassing of acidic magma. However, in the growth of quartz of the late generation, the beginning of crystallization of which was about 200ºC, CO2-fluids were involved. They are products of degassing of basic magma, which also took part in the growth of crystals at higher temperatures (˃573ºC). Crystallization of minerals in chambers was long: from 1.75±0.10 billion years (age of protogenetic inclusions of zircon and uraninite in topaz crystals) to 1.39 billion years (age of galena inclusions in late-generation quartz). So, for the first time, it was substantiated that the duration of crystal growth in the chambers of Volyn pegmatites was at least 360±100 million years. Therefore, it is assumed that the growth of crystals in chambers Volyn pegmatites lasted for quite a long time.

Genetic discrimination of the Dingjiashan Pb-Zn deposit, SE China, based on sphalerite chemistry

The Dingjiashan Pb-Zn deposit (5.35 Mt Pb + Zn @ 1.14% Pb and 4.07% Zn) is hosted by pyroxene-dominated skarn occurring along the contact zones between Proterozoic quartz mica schist and marble in the central Fujian region of southeastern China. The ore genesis of Proterozoic volcanogenic massive sulfide (VMS) vs. Late Mesozoic skarn type has long been debated. In this study, two types of sphalerite (sphalerite I and sphalerite II) were identified based on the mineral assemblages in the sulfide stage of the Dingjiashan deposit. Sphalerite I (including sphalerite Ia and sphalerite Ib subtypes), with a dark gray-blue to black coloring, is predominantly associated with pyrrhotite, whereas sphalerite II (including sphalerite IIa and sphalerite IIb subtypes) shows a light to dark gray-blue coloring and is mainly associated with galena and chalcopyrite. Geological features indicate that sphalerite I predates sphalerite II. Representative time-resolved depth profiles and mapping images based on the LA-ICP-MS method, coupled with inter-element correlation analyses, collectively illustrated that: 1) Fe, Mn, Cd, Co, In, Ga and Ge are present in solid solution; 2) Cu may occur both as solid solution and as micro-inclusions; 3) Ag, Pb and Bi may be intimately associated with galena inclusions hosted by sphalerite. The characteristics of trace and minor elements (such as Fe, Mn, In, Co, Ga, Ge, etc.), along with the results of GGIMFis geothermometer studies, indicate that the main mineralization stage occurred at high-temperature conditions (>300 °C). Compared to Pb-Zn deposits (including 6 VMS deposits and 9 skarn deposits) worldwide, sphalerite from the Dingjiashan Pb-Zn deposit exhibits similar ore-forming temperatures and trace/minor element compositions to those from skarn deposits, but is different to those from VMS deposits. This finding is of great significance for further exploration in the Dingjiashan deposit and—more broadly—the entire central Fujian region. It also provides an important future guide for the differentiation of VMS and skarn deposits.

Distribution of trace elements in sulfides from Deyin hydrothermal field, Mid-Atlantic Ridge – Implications for its mineralizing processes

Knowledge about the trace element distribution in sulfides is the key for understanding the trace metal inventory during the formation of the volcanic massive sulfide deposits on the seafloor. The distribution of trace metals in sulfides reflects changes in the physicochemical conditions and precipitation processes during precipitation. Hydrothermal black smoker samples of this study originate from the southern Mid-Atlantic (TVG02, TVG06) and can be classified into two types: (1) (Fe-Zn) sulfides consisting predominantly of pyrite and sphalerite, with minor chalcopyrite, isocubanite, and galena and (2) (Fe-Cu) sulfides, which contain mainly pyrite and chalcopyrite, with rare isocubanite and sphalerite. The sulfide samples were analyzed by electron microprobe for major elements, and by laser ablation inductively coupled plasma mass spectrometry, focused ion beam technique and transmission electron microscopy for in situ trace elements. The data reveal complex hydrothermal processes in high- and low- temperature fluids. Colloform and dendritic pyrite from (Fe-Zn) sulfides are enriched in Mn, Tl, As, V, Pb, and Zn, indicating precipitating from a rapid mixture of low temperature fluids (100–250 °C) with seawater. A continuous enrichment of incompatible elements (Pb and Zn) at the interface of growing pyrite with fluid finally leads to the nucleation and precipitation of sphalerite and galena, and results in the enrichment of As, Hg, Pb, Au, Ag, and Cd in sphalerite micro-inclusions which are hosted in colloform pyrite at low temperature. Galena inclusions occur in the pores and the interstices of sphalerite grains and formed by the enrichment of Pb in the hydrothermal fluid at low-temperature (<250 °C). High Cu, As, Ag, Au, and Sb concentrations in colloform sphalerite indicate a medium to low formation temperature (350–200 °C). Copper, Sb, Se, and Sn enrichments in coarse-grained sphalerite indicate medium temperature hydrothermal fluids. Idiomorphic pyrite and chalcopyrite have high Se and Co contents and indicate precipitaion from high-temperature (>300 °C) fluids.

Distribution of trace elements in willemite from the Belgium non-sulphide deposits

Samples of willemite (Zn2SiO4) mineralization from the historical non-sulphide Zn–Pb deposits of La Calamine (eastern Belgium) have been recovered from collections of the Geological Survey of Belgium. Textural and chemical analyses are used to evaluate the critical element distribution (Ge, In, Ga) and deportment. willemite occurs as a variety of types that continuously formed between the protore stage (sulphides) and the late supergene stage (carbonates and hydrated phases). Different types of willemite may be distinguished on the basis of their shape and zoning characteristics, supporting a polyphase non-sulphide mineralization after the protore stage. This is also marked by a significant change of major-element compositions in the late generation of willemite. Laserablation inductively coupled plasma mass-spectrometry (LA-ICP-MS) measurements of minor and trace elements also reveal a strong variability between the different willemite types, although no straightforward relation with the shape of willemite crystals or their zoning is demonstrated. Among the trace elements, we note anomalous high contents of P, Cd, As, Pb, Ag and Sb, the three latter ones being related to tiny galena inclusions. While Ga and In contents are very low (less than 4 ppm) or below detection limits, respectively, significant Ge contents up to 250 ppm were measured. Such contents are consistent with values reported from willemite mineralization throughout the world. The concentrations measured in willemite are similar to those in sphalerite (averaging 250 ppm), supporting a role as precursor for sphalerite. However, the supergene origin of willemite in Belgian deposits is controversial and the influence of low-temperature hydrothermal fluids for willemite precipitation cannot be ruled out. This also questions the origin of Ge further incorporated in zinc silicates.

Mineral chemistry of the Xiasai Ag–Pb–Zn deposit in the central Yidun Terrane, SW China: Insight into Ni–Ag–Bi mineralization and formation conditions

Sulfides and sulfosalts are major ore minerals for most of Ag–Pb–Zn deposits and can be used to study enrichment and distribution of ore-forming elements and formation conditions. The Xiasai Ag–Pb–Zn deposit (Zn 0.141 Mt @ 4.30%, Pb 0.132 Mt @ 4.03%, Ag 1028 t @ 337.8 g/t, Cu 10058 t @ 0.56%, and Sn 20000 t @ 0.75%) is a hydrothermal vein-type deposit in the central Yindun Terrane, SW China. It consists of proximal quartz-cassiterite veins and distal Ag–Pb–Zn sulfide veins to a Cretaceous monzogranite. Three successive mineralization sub-stages are recognized for Ag–Pb–Zn veins, i.e., arsenopyrite + coarse-grained pyrite (Py1) + pyrrhotite, sphalerite + chalcopyrite + fine-grained pyrite (Py2), and silver-minerals + native bismuth + galena.Nickel-minerals, such as breithauptite and ullmannite were identified as inclusions hosted within pyrrhotite using Energy Dispersive X-ray Spectroscopy (EDS) and Electron probe microscopy (EPM) analysis and mapping. Trace amounts of invisible silver have been detected in chalcopyrite and galena, whereas a significant amount of silver is incorporated in pyrargyrite, freibergite, miargyrite, and electrum as intimate intergrowths with galena or inclusions within galena. A high content of invisible bismuth is detected within galena (0.21–16.95 wt%), as well as numerous grains of native bismuth occur as inclusions in galena. Based on the Bi concentrations determined and the modal composition a large-sized bismuth deposit would be estimated with about 23,800 t of Bi resource. The presence of nickel-minerals and native bismuth, together with Zn/Cd ratios (58–151) of sphalerite, indicate that the ore-forming materials are derived from the Xiasai monzogranite.Based on mineral assemblages and chemical features for sulfides and sulfosalts, the formation of Ag–Pb–Zn ores was triggered by a decrease in temperature, fs2, fO2, and sulfidation. The early episode of arsenopyrite, Py1, pyrrhotite, and nickel-minerals formed at temperature of 320–470°C, lower fs2 and decreasing sulfidation conditions from low alkaline fluids. In contrast, the late episode of silver-minerals, native bismuth, and galena deposited at 160–270 °C with a lower fs2 state and neutral or acidic pH. However, a slight increase of fs2, fO2, and sulfidation (intermediate sulfidation) occurred during precipitation of Zn–Cu.

Минералогия аллювиальных отложений Авзянского золоторудного района (Южный Урал)

The Avzyan gold region is located within the Bashkirian anticlinorium and includes lode gold deposits and placers. The Gorny Priisk, Bogryashka and Ulyuk-Bar gold deposits are hosted in the Riphean metamorphosed carbonaceous sequence. The article describes the mineralogy of the heavy concentrates from alluvial sediments of the streams of Bolshoy Avzyan basin which drains the Gorny Priisk, Bogryashka and Ulyuk-Bar gold ore deposits. The comparison of mineralogical and chemical feature of the studied heavy concentrates is done. Samples and Methods. Samples from the streams were collected every 50-100 m. Hand specimens of ore and host rocks from the lode gold deposits were collected from outcrops and dumps. The content of metals in the heavy concentrates estimated using X-ray fluorescence analyzer Innov-X alfa. Chemical composition of the accessory minerals was studied using electron microscope Vega-3 Tescan with EDA X-Act Oxford. Discussion and Results. The source of the alluvial sediments was the lode gold deposits located in the immediate vicinity of placers. Heavy concentrates of the Kamenny stream are characterized by a high content of As and Cu while ones of the Bogryashka and Bolshoy Klyuch streams show a high content of Cr and Ba. Goethite is major ore mineral for all studied samples. Ilmenite, rutile, epidote and barite are also widespread in the samples from the Bogryashka and Bolshoy Klyuch streams. Native gold is present in the sediments of all studied stream. The greatest number of gold grains was found in the samples from the Bolshoy Klyuch stream. The weak roundness of the golds and the presence of unoxidized sulfides (pyrite, chalcopyrite and pyrrhotite) indicate a relatively small age of placers. Monazite and xenotime morphology suggests autigenic catagenetic and/or metamorphic origin. Monazite contains (apfu) Ce (0.27-0.56), Nd (0.10-0.37) and La (0.09-0.33), minor Pr, Sm, Gd, Eu and Dy; ThO 2 up to 9.78 wt. % (0.08 apfu). It is similar with monazite composition from other streams of the east part of the Bashkirian anticlinorium and can be evidence of their similar origin. Xenotime contains major Gd, Dy and Er and minor Tb and Ho. Xenotime from the Bogryashka stream is characterized by the increased concentration of (apfu) Gd (0.10-0.24), Nd (0.01-0.02), Sm (0.03-0.06), Eu (0.02-0.06) and absence of Ho and Yb. Xenotime composition from the Kamenny and Bolshoy Klyuch streams is similar with ones from east part of the Bashkirian anticlinorium. Galena inclusions in REE phosphates, monazite inclusions in goethite and xenotime inclusions in pyrite can be evidence about similar conditions and time of formation gold-sulfide and REE mineralization.

Chemical and textural interpretation of late-stage coffinite and brannerite from the Olympic Dam IOCG-Ag-U deposit

AbstractThe Olympic Dam iron-oxide copper-gold-silver-uranium deposit, South Australia, contains three dominant U minerals: uraninite; coffinite; and brannerite. Microanalytical and petrographic observations provide evidence for an interpretation in which brannerite and coffinite essentially represent the products of U mineralizing events after initial deposit formation at 1.6 Ga. Marked compositional and textural differences between the various types of brannerite and coffinite highlight the role of multiple stages of U dissolution and reprecipitation.On the basis of petrography (size, habit, textures and mineral associations) and compositional variation, brannerites are divided into four distinct groups (brannerite-A, -B, -C and -D), and coffinite into three groups (coffinite-A, -B and -C). Brannerite-A ranges in composition from what is effectively uraniferous rutile to stoichiometric brannerite, and has elevated (Mg +Mn + Na + K) and (Fe + Al) compared to other brannerite types. It displays the most diverse range of morphologies, including complex irregular-shaped aggregates, replacement bands, and discrete elongate seams. The internal structure of brannerite-A consists of randomly-oriented hair-like needles and blades. Brannerite-B (&gt;5 μm in size) is generally prismatic and typically associated with baryte and REY minerals (REE+Y= REY). Brannerite-C and -D are both associated with Cu-(Fe)-sulfides and are typically composed of irregular masses and blebs (10–50 μm in size) with a more uniform or massive internal structure. Brannerite-D is distinct from -C and always contains inclusions of galena. Brannerite-B to -D all contain elevated ΣREY, with brannerite-B and -C having elevated As, and brannerite-D having elevated Nb.All coffinite is typically globular (each globule is 2–10 μm in size) to collomorphic in appearance. Coffinite-A ranges from discrete globules to collomorphic bands completely encompassing quartz. Coffinite-B is always found with uraninite, and includes collomorph coffinite enveloped by massive uraninite, as well as aureoles of coffinite on the margins of uraninite crystals. Coffinite-C is associated with brannerite and REY minerals. The majority of coffinite is heterogeneous.Brannerite and coffinite have probably precipitated as part of a late-stage hydrothermal U-event, which might have involved the dissolution and/or reprecipitation of earlier precipitated uraninite, or could represent the products of a later U mineralizing event. Evidence which supports formation of late-stage coffinite and brannerite includes: (1) low-Pb contents of both minerals; (2) coffinite is commonly found on the edges of uraninite, implying later deposition; and (3) coffinite is often found on the edge of brannerite aggregates, suggestive of brannerite precipitation occurred before coffinite. Moreover, there are many features (e.g. banding, scalloped edges, alteration rinds, variable compositions etc.) indicative of hydrothermal alteration processes.

The forms of occurrence and geochemistry of sulfides in hard coal deposits of the Libiąż Beds in the Upper Silesian Coal Basin, Southern Poland

Samples of coal from the eastern part of the Upper Silesian Coal Basin, between Jaworzno and Libiąz, were collected from test boreholes and underground excavations in the Janina Coal Mine, southwest Poland. The No. 111-119 hard coal seams are in the upper part of the Cracow Sandstone Series (the Libiąz Beds, Westphalian D). Macroscopically, iron sulfides (pyrite and marcasite) found in hard coal seams are usually in vein and impregnation forms. On the basis of microscopic observations, the following forms of iron sulfides occurrence in the studied coal were observed: framboidal pyrite, euhedral crystals, skeletal and massive vein forms, or pocket-like (impregnation) forms. On the basis of SEM-EDS analysis and X-ray diffraction it can be stated that the iron sulfides observed in coal are a mixture of pyrite and marcasite. WDS analysis in the micro area revealed the chemical composition of sulfides. The iron sulfides contain admixtures of Pb, Hg, Zn, Cu, Au, Ag, Sb, Co, and Ni. There was no As and Cd found in the examined minerals. It has been shown that the tested iron sulfides do not include significant admixtures. There is only a slight enrichment in lead in the vein forms of sulfides. In addition to the iron sulfides, individual inclusions of galena and sphalerite within the pyrite and marcasite have been observed.

Nakhlak carbonate-hosted Pb[sbnd](Ag) deposit, Isfahan province, Iran: a geological, mineralogical, geochemical, fluid inclusion, and sulfur isotope study

The Upper Cretaceous Nakhlak epigenetic vein-type Pb(Ag) deposit is located 55km northeast of the town of Anarak in Isfahan Province, Iran. The deposit contains 7Mt of galena-barite ore with an average grade of 8.33% Pb, 0.38% Zn, and 72ppm Ag. The ore mineralization occurs as stratabound, epigenetic, steeply dipping, east-west–trending veins in faulted- or fracture-controlled Upper Cretaceous Sadar carbonates. Galena and barite are the primary minerals. Minor sphalerite, tennantite-tetrahedrite, pyrite, and chalcopyrite occur as inclusions in galena. Cerussite with minor amounts of anglesite and plattnerite formed in the oxidized supergene zone. The ore and ore-related minerals were deposited in the hydrothermally dolomitized carbonate host rock containing saddle-shaped dolomite. Geochemically, the dolomitized carbonate host rocks are enriched in MgO, Fe2O3, MnO, Pb, Zn, and Ba, but depleted in CaO. The galena concentrate contains high values of Ag (932ppm), Sb (342ppm), Cu (422ppm), As (91ppm), and Zn (296ppm); the presence of these trace elements indicates a low-temperature type of galena mineralization. This interpretation is corroborated by fluid inclusions containing 12.98wt.% NaCl equivalent salinity; the inclusions homogenize at the low temperature of about 152.1°C. The similarity between δ34S(V-CDT) values in Nakhlak barite and Permian–Triassic δ34S marine sulfate values indicates that the Nakhlak sulfur was probably provided from evaporates of Permian–Triassic age. The δ34S(V-CDT) values of galena and barite samples occupy the ranges of −1.04‰ to +8.62‰ and +10.95‰ to +13.71‰, respectively, and are similar to Mississippi Valley–type (MVT) deposits. The low-temperature basinal fluids, evaporate-originated sulfur, and fault- or fracture-controlled galena-rich veins in the Nakhlak deposit resemble the type of geological features documented in Pb-rich MVT deposits.

Uraninite from the Olympic Dam IOCG-U-Ag deposit: Linking textural and compositional variation to temporal evolution

The Olympic Dam IOCG-U-Ag deposit, South Australia, the world’s largest known uranium (U) resource, contains three main U-minerals: uraninite, coffinite, and brannerite. Four main classes of uraninite have been identified. Uraninite occurring as single grains is characterized by high-Pb and ΣREE+Y (ΣREY) but based on textures can be classified into three of these classes, typically present in the same sample. Primary uraninite (Class 1) is smallest (10–50 μm), displays a cubic-euhedral habit, and both oscillatory and sectorial zoning. “Zoned” uraninite (Class 2) is coarser, sub-euhedral, and combines different styles of zonation in the same grain. “Cobweb” uraninite (Class 3) is coarser still, up to several hundred micrometers, has variable hexagonal-octagonal morphologies, varying degrees of rounding, and features rhythmic intergrowths with sulfide minerals. In contrast, the highest-grade U in the deposit is found as micrometer-sized grains to aphanitic varieties of uraninite that form larger aggregates (up to millimeter) and vein-fillings (massive, Class 4) and have lower Pb and ΣREY, but higher Ca. Nanoscale characterization of primary and cobweb uraninite shows these have defect-free fluorite structure. Both contain lattice-bound Pb+ΣREY, which for primary uraninite is concentrated within zones, and for cobweb uraninite is within high-Pb+ΣREY domains. Micro-fractured low-Pb+ΣREY domains, sometimes with different crystal orientation to the high-Pb+ΣREY domains in the same cobweb grain, contain nanoscale inclusions of galena, Cu-Fe-sulfides, and REY-minerals. The observed Pb zonation and presence of inclusions indicates solid-state trace-element mobility during the healing of radiogenic damage, and subsequent inclusion-nucleation + recrystallization during ![Formula][1] -driven percolation of Cu-bearing fluid. Tetravalent, lattice-bound radiogenic Pb is proposed based on analogous evidence for U-bearing zircon. Calculating the crystal chemical formula to UO2 stoichiometry, the sum of cations (M*) is ~1 for most classes, but the presence of mono-, di-, and trivalent elements (ΣREY, Ca, etc.) drive stoichiometry toward hypostoichiometric M*O2–x. In the absence of measured O and constraints of hypostoichiometric fluorite-structure, charge-balance calculations showing O deficit in the range 0.15–0.36 apfu is compensated by assumption of mixed U oxidation states. Crystal structural formulas show up to 0.20 apfu Pb and 0.25 apfu ΣREY in Classes 1–3, while for Class 4, these are an order of magnitude less. Low-Pb and ΣREY subcategories of Classes 2 and 3 are similar to massive uraninite with ~0.2 apfu Ca. Other elements (Si, Na, Mn, As, Nb, etc.), show two distinct geochemical trends: (1) across Classes 1–3; and (2) Class 4, whereby low-Pb+ΣREY sub-populations of Classes 2 and 3 are part of trend 2 for certain elements. Plots of alteration factor (CaO+SiO2+Fe2O3) vs. Pb/U suggest two uraninite generations: early (high-Pb+ΣREY, Classes 1–3); and late (massive, Class 4). There is evidence of Pb loss from diffusion, leaching and/or recrystallization for Classes 2–3 (low-Pb+ΣREY domains). Micro-analytical data and petrographic observations reported here, including nanoscale characterization of individual uraninite grains, support the hypothesis for at least two main uraninite mineralizing events at Olympic Dam and multiple stages of U dissolution and reprecipitation. Early crystalline uraninite is only sparsely preserved, with the majority of uraninite represented by the massive-aphanitic products of post-1590 Ma dissolution, reprecipitation, and possibly addition of uranium into the system. Coupled dissolution-reprecipitation reactions are suggested for early uraninite evolution across Classes 1 to 3. The calculated oxidation state [U6+/(U4++U6+)] of the “early” and “late” populations point to different conditions at the time of formation (charge compensation for ΣREY-rich early fluids) rather than auto-oxidation of uraninite. Late uraninites may have formed hydrothermally at lower temperatures ( T < 250 °C). [1]: /embed/mml-math-1.gif

(Pb–Sb)-bearing sphalerite from the Čumavići polymetallic ore deposit, Podrinje Metallogenic District, East Bosnia and Herzegovina

Čumavići is a medium– to low–temperature hydrothermal Sb–Zn–Pb–Ag polymetallic vein–type ore deposit in the Srebrenica orefield, part of the Podrinje Metallogenic District, Eastern Bosnia and Herzegovina. The ore deposit occurs in the form of simple and complex veins along faults and fractures, as well as stockworks and disseminations hosted within Neogene volcanic rocks (pyroclastics and andesite lavas of calc–alkaline affinity). The deposit comprises sulfides (sphalerite, galena, stibnite, pyrite, marcasite, chalcopyrite, arsenopyrite, gudmundite, safflorite, löllingite, gersdorffite and acanthite), sulfosalts (berthierite, geocronite, boulangerite, semseyite, plagionite, jamesonite, bournonite, twinnite, andorite, fizéliyte, Ag–bearing tetrahedrite, stephanite, polybasite, pyrargyrite and argyrodite), native gold and silver, tungstates (hübnerite), oxides, and gangue quartz, chalcedony, Mn–siderite, anglesite, smithsonite, fluorite, gypsum and ludlamite. Three generations of sphalerite are recognized in the Čumavići deposit, evolving from Fe–rich to Fe–poor. The most common are yellowish to colorless Fe–poor varieties. Electron Probe Microanalyses of sphalerite free of micro–inclusions of galena and Pb–Sb-sulfosalts revealed wide compositional variations in minor- and trace–element contents (e.g., Fe, Cd, Mn, Cu, Sn, As, and In). Of particular interest are the lead and antimony content of sphalerite, which vary from 0.10 to 3.08, and 0.02 to 1.62wt.%, respectively. Lead– and Pb–Sb-rich zones are the most common in sphalerite, while individual Sb–bearing zones are rare. These zones have fan–like forms with circular to wave-like, micron–scale bands, filled with galena or Pb–Sb sulfosalts. In the Pb–Sb zones, the Sb/Pb atomic ratio ranges between 0.3 and 1.5, similar to ratios between geocronite and jamesonite, thus suggesting the presence of micro– to nano–scale inclusion of sulfosalts within the sphalerite. The mean composition of all sphalerite samples is (Zn0.78–0.99,Fe<0.01–0.21,Cu0.00–0.02,Pb<0.01–0.01,Cd<0.01–0.01,Sb<0.01–0.01,Mn<0.01–0.01)∑0.97–1.03S0.97–1.08 (Sn and As atomic proportions are <0.01 apfu). In all sphalerite samples, excellent negative correlations have been determined between Fe and Zn, and ∑(Fe+Sb) and Zn. The studied mineralization shares many mineralogical and geological characteristics in common to polymetallic Sn–Ag–Sb deposits in Bolivia and elsewhere.

Gold grade variation and particle microchemistry in exploration pits of the Batouri gold district, SE Cameroon

The Batouri area hosts lode-gold mineralization under several-m-thick lateritic cover. Pitting to bed rock on a geochemical Au anomaly defined from previous reconnaissance soil sampling identified five horizons ranging from saprock at the base to laterite at the top. Analysis of bulk samples from each horizon by fire assay shows that most of the horizons are barren although 119 ppb and 48 ppb Au values were obtained from one laterite horizon and one saprolite horizon, respectively, from two separate pits. All the horizons were panned and particulate gold was also recovered only from these two horizons. The gold grains from both horizons are morphologically and compositionally indistinguishable with rare quartz, pyrite and galena inclusions. The grains have irregular, sub-rounded, bean to elongated shapes and they show a remarkable core–rim zonation. Electron microprobe analysis of the grains recorded high gold content in the rims (86.3–100 wt%) and along fissures within the grains (95.1–100 wt%). The cores are relatively Ag rich (11.8–14 wt% Ag) while the rims (0.63–13.7 wt% Ag, most of the values fall within the lower limit of this range) and fissures (0.03–5.02 wt% Ag) are poor in Ag. The low Ag concentration in the rims and along fissures is attributed to preferential leaching of Ag; a process recognized in gold grains and platiniferous alloys from alluvia. The core composition of the grains is similar to that of primary gold composition in the bedrock. These results show that gold in the soil is relic particulate gold derived from the primary source with no evidence of secondary gold precipitation in the weathering cycle. In all the pits no horizon was systematically enriched in gold suggesting there has been no chemical remobilization of gold in this environment. Rather the dispersion of gold here is in the particulate form. Therefore combining particulate gold features with assay data is relevant to exploration in such tropical environments.

Unraveling the Western Churchill Province Paleoproterozoic Gold Metallotect: Constraints from Re-Os Arsenopyrite and U-Pb Xenotime Geochronology and LA-ICP-MS Arsenopyrite Trace Element Chemistry at the BIF-Hosted Meliadine Gold District, Nunavut, Canada

The gold endowment of the western Churchill Province is conventionally attributed to reworking and attendant metamorphism during the Trans-Hudson Orogeny (1.9–1.8 Ga). The Meliadine gold district is regarded as a type example of this inferred Paleoproterozoic gold metallotect and also represents one of Canada’s largest emerging orogenic greenstone- and banded iron formation (BIF)-hosted gold districts (2.8 Moz contained Au in reserves and total resource of 5.8 Moz Au). The largest gold deposits are cospatial with the Pyke fault and associated quartz (± ankerite) veining, which cuts Neoarchean (ca. 2.66 Ga) plutonic and supracrustal rocks comprising the Rankin Inlet greenstone belt. Meliadine gold occurs as inclusions within idioblastic arsenopyrite crystals, at sulfide crystal boundaries, and/or as sulfide fracture fills in hydrothermally altered, sulfidized, and veined BIF. Clusters of gold, Bi-Mo telluride, chalcopyrite, and galena inclusions characterize high-grade ore zones and are spatially associated with sieve-textured arsenopyrite domains. These microtextural relationships suggest that incipient sulfide recrystallization liberated gold, which, along with other precious and base metals, was redistributed during late, fluid-assisted and deformation/metamorphic-driven remobilization. Late precious and base metal enrichment is also demonstrated by in situ laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) arsenopyrite mapping. Hydrothermal xenotime crystals occur with gold in low-strain microtextural sites and yield U-Pb ages at ca. 1.86 Ga, suggesting that remobilization was concomitant with Trans Hudson orogenesis. New Re-Os arsenopyrite model ages range from 2.3 to 1.8 Ga and document a hitherto unrecognized, pre-1.86 Ga hydrothermal activity. The range of Re-Os model ages tends to support partial open-system behavior and/or mixing of disparate arsenopyrite generations that are evident from microtextural observations and in situ LA-ICP-MS element mapping. Replicate analyses of the two most rhenium rich arsenopyrite samples yield reproducible Re-Os model ages at ca. 2.27 and 1.90 Ga. These rhenium-rich samples are also gold poor and likely yield ages that predate gold remobilization and subsequent enrichment along arsenopyrite crystal boundaries and fractures. We suggest that pre-1.86 Ga hydrothermal activity was likely critical to the gold endowment of the district, but is obscured by reworking during the later stages of the Trans-Hudson Orogeny at 1.86 Ga. If correct, these new ages imply that the Paleoproterozoic gold metallotect, which is recorded across the western Churchill Province, in fact comprises multiple, temporally distinct gold events. Differentiating between disparate Paleoproterozoic gold events represents a critical step for effective mineral exploration in the western Churchill Province and at other reworked Archean terranes.

Fluid mixing forms basement-hosted Pb-Zn deposits: Insight from metal and halogen geochemistry of individual fluid inclusions

Fluid mixing across unconformities between crystalline basement and overlying sedimentary basins is commonly invoked as an efficient chemical mechanism for ore deposition, but the origin of basement brines and the process of ore formation have rarely been linked by direct evidence. Using laser ablation–inductively coupled plasma–mass spectrometry microanalysis of individual fluid inclusions with an improved detection approach for anion components, we determined simultaneously the ore metal concentrations and the Cl/Br ratio in texturally well constrained inclusion assemblages from a basement-hosted quartz-fluorite-barite-Pb-Zn vein system. An inverse correlation between the Pb + Zn concentrations and the Cl/Br mass ratios in the fluid inclusions provides clear evidence for mixing of a basement-derived metal-rich brine and a metal-poor formation water that acquired its salinity from halite dissolution in Triassic evaporites of the sedimentary cover. This mixing of two distinct brines with comparable salinity is recorded during the growth of individual quartz crystals containing small galena inclusions, demonstrating the transient and episodic nature of fluid mixing during mineral deposition.

New source of unavoidable ions in galena flotation pulp: Components released from fluid inclusions

The present work investigated the trace and component release of fluid inclusions in natural pure galena. The investigation results indicated that the composition of the inclusion trace was characterized by a lower Pb content compared to the theoretical composition of galena; nonetheless, these inclusions were rich in lead and chlorine ion. The inclusions were liberated through a grinding process where their compositions were released into solution. It was found that the lead concentrations (CPbT) released from the inclusions through the grinding process reached 8.25×10−6mol/L in the experiment with conditions of 2g galena placed into 40ml pure deionized water under an inert environment, which was much higher than the CPbT found through experimental dissolution (1.12×10−6mol/L). Therefore, it was concluded that the release of Pb from the fluid inclusions in galena was an important new source of the Pb concentration in the solution. This finding sheds new light on the source of unavoidable ions in the flotation pulp. The residual position domain after the release of the inclusions causes the morphology difference in the galena surface composition and roughness. This study provided a new understanding of the unavoidable ion source that is found in the flotation theory and environmental geochemistry.

Hydrothermal uranium-base metal mineralization of the Jánská vein, Březové Hory, Příbram, Czech Republic: lead isotopes and chemical dating of uraninite

The Janska vein is one of the important veins of Březove Hory mining district (central Bohemia, Czech Republic). Base metals were mined here since 14th century and uranium ore during late 1950s. Uranium mineralization is younger than most of the base metal mineralization according to macroscopic and microscopic study. Most specimens of uraninite, obtained from archive, contain more or less abundant galena inclusions. Galena of this type is non-radiogenic as indicated by its Pb isotopic composition (ICP-MS). Its origin can be explained by remobilisation of the older base-metal mineralization during the younger, uranium-bearing mineralization event. The amount of radiogenic Pb in uraninite fluctuates from 48 up to 89.8 %. The age of theoretical end member of uraninite, calculated statistically from all measured data (for intersection 208Pb/206Pb = 0), is 269.8 err 20.3 Ma. The only uraninite grain without galena inclusions yielded an age of 263.2 err 8.9 Ma by chemical dating using electron microprobe. The calculated age of the uranium mineralization is in agreement with published data for other uranium deposits genetically associated with the Central Bohemian Plutonic Complex.