Pb-Zn Ore Deposits Research Articles

Ore genesis of Pb–Zn deposits in the Nappe zone of Northern Tunisia: Constraints from Pb–S–C–O isotopic systems

The Jalta and Jebel Ghozlane ore deposits are located in the extreme North of Tunisia, within the Nappe zone. The mineralization of Jalta, hosted in Triassic dolostones and the overlying Mio-Pliocene conglomerates, consists of abundant galena, barite, and cerussite with accessory sphalerite, pyrite, and jordanite. At Jebel Ghozlane, large Pb–Zn concentrations occur in the Triassic dolostones and Eocene limestones. The mineral association consists of galena, sphalerite, barite, and celestite and their oxidation products (cerussite, smithsonite, and anglesite). Lead isotope ratios in galena from both districts are relatively homogeneous ( 206Pb/ 204Pb = 18.702–18.823, 207Pb/ 204Pb = 15.665–15.677, 208Pb/ 204Pb = 38.725–38.875). The δ 34S values for sulfates from both areas (+ 12.2 to + 16.2‰ at Jalta and + 14.3 to + 19.4‰ at Jebel Ghozlane) are compatible with a derivation of sulfur from marine sulfates, possibly sourced from the Triassic evaporites. The δ 34S values of the sulfides have a range between − 10 and + 12.5‰ at Jalta, and between − 9.1 and + 22.1‰ at Jebel Ghozlane. The large range of values suggests reduction of the sulfate by bacterial and/or thermochemical reduction of sulfate to sulfur. The high δ 34S values of sulfides require closed-system reduction processes. The isotopically light carbon in late calcites (− 6.3 to − 2.5‰) and authigenic dolomite (− 17.6‰) suggests an organic source of at least some of the carbon in these samples, whereas the similarity of the δ 18O values between calcite (+ 24.8‰) and the authigenic dolomite (+ 24.7‰) of Jalta and their respective host rocks reflects oxygen isotope buffering of the mineralizing fluids by the host rock carbonates. The secondary calcite isotope compositions of Jalta are compatible with a hydrothermal fluid circulation at approximately 100 to 200 °C, but temperatures as low as 50 °C may be indicated by the late calcite of Jebel Ghozlane (δ 18O of + 35.9‰). Given the geological events related to the Alpine orogeny in the Nappe zone (nappe emplacement, bimodal volcanism, and reactivation of major faults, such as Ghardimaou-Cap Serrat) and the Neogene age of the host rocks in several localities, a Late-Miocene age is proposed for the Pb–Zn ore deposits considered in this study. Remobilization of deep-seated primary deposits in the Paleozoic sequence is the most probable source for metals in both localities considered in this study and probably in the Nappe zone as a whole.

Does biodiversity of macroinvertebrates and genome response of Chironomidae larvae (Diptera) reflect heavy metal pollution in a small pond?

The investigation was carried out on a small pond situated on a recent mine spoil at Bolesław in the Olkusz region with Zn-Pb ore deposits. Water of the pond had pH7.2-8.5 and low concentrations of heavy metals. Concentrations of Pb (487μgg( - 1)) and Zn (1,991μgg( - 1)) in the sediment were very high and potentially could lead to toxicological effects. In the pond, 48 taxa of macroinvertebrates belonging to Oligochaeta and water stages of Ephemeroptera, Odonata, Megaloptera, Trichoptera, Heteroptera, Coleoptera and Diptera (mainly Chironomidae family) were found. The influence of heavy metals on macroinvertebrates diversity was not found. Effect of heavy metal pollution was observed on the appearance of chromosome aberrations in the polytene chromosomes of Chironomidae larvae. It was manifested by two ways: (1) in Kiefferulus tendipediformis and Chironomus sp. chromosome rearrangements in fixed state (tandem fusion and homozygous inversions), indicated intensive process of speciation; (2) in Chironomus sp., K. tendipediformis, Glyptotendipes gripekoveni (Chironomidae) somatic chromosome rearrangements (inversions, deficiencies, specific puffs, polyploidy) affected few cells of every individual. The somatic functional and structural alterations in Chironomidae species are particular suitable as biomarkers-they can be easily identified and used for detecting toxic agents in the environment.

Geochemistry of trace metals and Pb isotopes of sediments from the lowermost Xiangjiang River, Hunan Province (P. R. China): implications on sources of trace metals

This paper reports a geochemical study of trace metals and Pb isotopes of sediments from the lowermost Xiangjiang River, Hunan province (P. R. China). Trace metals Ba, Bi, Sc, V, Cr, Mn, Co, Ni, Cu, Zn, Mo, Cd, Sn, Sb, Pb, Tl, Th, U, Zr, Hf, Nb and Ta were analyzed using ICP-MS, and Pb isotopes of the bulk sediments were measured by MC-ICP-MS. The results show that trace metals Cd, Bi, Sn, Sc, Cr, Mn, Co, Ni, Cu, Zn, Sb, Pb and Tl are enriched in the sediments. Among these metals, Cd, Bi and Sn are extremely highly enriched (EF values >40), metals Zn, Sn, Sb and Pb significantly highly (5 < EF < 20), and metals Sc, Cr, Mn, Co, Ni, Cu and Tl moderately highly (2 < EF < 5) enriched in the river sediments. All these metals, however, are moderately enriched in the lake sediments. Geochemical results of trace metals Th, Sc, Co, Cr, Zr, Hf and La, and Pb isotopes suggest that metals in the river sediments are of multi-sources, including both natural and anthropogenic sources. Metals of the natural sources might be contributed mostly from weathering of the Indosinian granites (GR) and Palaeozoic sandstones (PL), and metals of anthropogenic sources were contributed from Pb–Zn ore deposits distributed in upper river areas. Metals in the lake sediments consist of the anthropogenic proportions, which were contributed from automobile exhausts and coal dusts. Thus, heavy-metal contamination for the river sediments is attributed to the exploitation and utilization (e.g., mining, smelting, and refining) of Pb–Zn ore mineral resources in the upper river areas, and this for the lake sediments was caused by automobile exhausts and coal combustion. Metals Bi, Cd, Pb, Sn and Sb have anthropogenic proportion of higher than 90%, with natural contribution less than 10%. Metals Mn and Zn consist of anthropogenic proportion of 60–85%, with natural proportion higher than 15%. Metals Sc, Cr, Co, Cu, Tl, Th, U and Ta have anthropogenic proportion of 30–70%, with natural contribution higher than 30%. Metals Ba, V and Mo might be contributed mostly from natural process.

Trace Elements and Rare Earth Elements of Sulfide Minerals in the Tianqiao Pb‐Zn Ore Deposit, Guizhou Province, China

Abstract:Trace elements and rare earth elements (REE) of the sulfide minerals were determined by inductively‐coupled plasma mass spectrometry. The results indicate that V, Cu, Sn, Ga, Cd, In, and Se are concentrated in sphalerite, Sb, As, Ge, and Tl are concentrated in galena, and almost all trace elements in pyrite are low. The Ga and Cd contents in the light‐yellow sphalerites are higher than that in the brown and the black sphalerites. The contents of Ge, Tl, In, and Se in brown sphalerites are higher than that in light‐yellow sphalerites and black sphalerites. It shows that REE concentrations are higher in pyrite than in sphalerite, and galena. In sphalerites, the REE concentration decreases from light‐yellow sphalerites, brown sphalerites, to black sphalerites. The ratios of Ga/In are more than 10, and Co/Ni are less than 1 in the studied sphalerites and pyrites, respectively, indicating that the genesis of the Tianqiao Pb–Zn ore deposit might belong to sedimentary‐reformed genesis associated with hydrothermal genesis. The relationship between LnGa and LnIn in sphalerite, and between LnBi and LnSb in galena, indicates that the Tianqiao Pb–Zn ore deposit might belong to sedimentary‐reformed genesis. Based on the chondrite‐normalized REE patterns, δEu is a negative anomaly (0.13–0.88), and δCe does not show obvious anomaly (0.88–1.31); all the samples have low total REE concentrations (&lt;3 ppm) and a wide range of light rare earth element/high rare earth element ratios (1.12–12.35). These results indicate that the ore‐forming fluids occur under a reducing environment. Comparison REE compositions and parameters of sphalerites, galenas, pyrites, ores, altered dolostone rocks, strata carbonates, and the pyrite from Lower Carboniferous Datang Formation showed that the ore‐forming fluids might come from polycomponent systems, that is, different chronostratigraphic units could make an important contribution to the ore‐forming fluids. Combined with the tectonic setting and previous isotopic geochemistry evidence, we conclude that the ore‐deposit genesis is hydrothermal, sedimentary reformed, with multisources characteristics of ore‐forming fluids.

Sulfur isotopic composition of the Tianqiao Pb-Zn ore deposit, Northwest Guizhou Province, China: Implications for the source of sulfur in the ore-forming fluids

The Tianqiao Pb-Zn ore deposit of Guizhou Province, China, is located in the mid-east of the Sichuan-Yunnan-Guizhou Pb-Zn-Ag multi-metallic mineralization area, which is representative of the Pb-Zn ore deposits in this area. It consists of three main orebodies, whose Pb+Zn reserves are more than 0.2 million ton. This paper analyzes the sulfur isotopic composition of these orebodies. The data show that the ore minerals (galena, sphalerite, pyrite) in these orebodies are enriched in heavy sulfur, with δ34SV-CDT values varying between 8.35‰ and 14.44‰, i.e. the δ34SV-CDT values of pyrite are between 12.81‰ and 14.44‰, the mean value is 13.40‰; the δ34SV-CDT values of sphalerite are range from 10.87‰ to 14.00‰, the mean value is 12.53‰; the δ34SV-CDT values of galena are range from 8.35‰ to 9.83‰, the mean value is 8.84‰, and they have the feature of δ34Spyrite>δ34Ssphalerite>δ34Sgalena, which indicates the sulfur isotope in ore-forming fluids has attained equilibrium. The δ34SV-CDT values of the deposit are close to those of sulfates from carbonate strata of different ages in the ore-field (15‰), which suggests that the sulfur in the ore-forming fluids should be derived from the thermo-chemical sulfate reduction of sulfates from the sedimentary strata.

Paleomagnetic dating of non-sulfide Zn-Pb ores in SW Sardinia (Italy): a first attempt

A first paleomagnetic investigation aimed at constraining the age of the non-sulfide Zn-Pb ore deposits in the Iglesiente district (SW Sardinia, Italy) was carried out. In these ores, the oxidation of primary sulfides, hosted in Cambrian carbonate rocks, was related to several paleoweathering episodes spanning from the Mesozoic onward. Paleomagnetic analyses were performed on 43 cores from 4 different localities, containing: a) non-oxidized primary sulfides and host rock, b) oxidized Fe-rich hydrothermal dolomites and (c) supergene oxidation ore («Calamine»). Reliable data were obtained from 18 samples; the others show uninterpretable results due to low magnetic intensity or to scattered demagnetization trajectories. Three of them show a scattered Characteristic Remanent Magnetization (ChRM), likely carried by the original (i.e. Paleozoic) magnetic iron sulfides. The remaining 15 samples show a well defined and coherent ChRM, carried by high-coercivity minerals, acquired after the last phase of counterclockwise rotation of Sardinia (that is after 16 Myr), in a time interval long enough to span at least one reversal of the geomagnetic field. Hematite is the main magnetic carrier in the limestone, whereas weathered hydrothermal dolomite contains goethite or a mixture of both. The results suggest that paleomagnetism can be used to constrain the timing of oxidation in supergene-enriched ores.

Roman road pollution assessed by elemental and lead isotope geochemistry in East Belgium

The ability of inorganic geochemistry to record environmental change and especially human impact has been evidenced by several studies across Europe, especially in peat, where it is possible to record the impact of agriculture, mining and other industries. However, despite the numerous investigations on the impact of ancient human activities such as ore mining and smelting, little attention has been paid to geochemistry as a tool to solve problems of palaeopollution in the surroundings of archaeological sites. This paper presents geochemical evidence of the impact of a possible early Roman road built in SE Belgian peatland. Increased Zn and Pb concentrations suggest that Pb–Zn ores were transported on the road. Lead isotope analyses suggest that these ores are locally derived, being compatible with those found in the nearby Pb–Zn ore deposits from East Belgium. Present results provide direct evidence that East Belgian Pb–Zn ores were already being mined during Roman times, i.e. earlier than previously suspected (i.e. 14th century) and that Zn appears to be relatively immobile here. On a broader scale, it also demonstrates that such an early road already had an impact on the environment in terms of metal pollution. This paper enlarges on the range of possibilities offered by geochemistry in the field of geoarchaeology.

Pb–Zn mineralization in a Miocene regional extensional context: The case of the Sidi Driss and the Douahria ore deposits (Nefza mining district, northern Tunisia)

The Sidi Driss and Douahria sulfide ore deposits and showings are located in the Nefza mining district, northern Tunisia. The ores are hosted within Upper Miocene (Messinian) basins, within carbonate lenses composed of Fe–Mn-enriched dedolomite partially or totally replaced by early barite and celestite. The ore mainly consists of galena and spherulitic/colloform sphalerite (partially replaced by later Fe-sulfides). It is present as disseminated or banded ores and has been deposited within the host-rock through dissolution/replacement process or through void infilling. The remaining voids are filled by late calcite/barite locally associated with a late oxidation event. In situ ion microprobe sulfur isotope analyses show significant variability for sphalerite (from − 43.9 to 1.2‰), galena (from − 30.3 to − 2‰) and marcasite δ 34S (from − 35.9 to 25.8‰). These values are interpreted as the result of (i) the mixing of two sulfur end-members in the mineralizing fluids, corresponding to different reduction processes (bacterially-mediated sulfate reduction and thermochemical sulfate reduction, with early celestite and barite and/or contemporaneous Messinian seawater, together with Triassic sulfate, as sulfur sources, and (ii) Rayleigh fractionation process in a closed system. Several arguments (Fe–Mn enrichment in early diagenetic carbonates, involvement of Messinian seawater as a sulfur source, low temperature of deposition and soft-style sedimentary figures within sulfides) suggest that the Sidi Driss and Douahria Pb–Zn ore deposits are syn-diagenetic. Moreover, the properties of the ore deposits, with Fe–Mn carbonates having a wider distribution than that of the base metal sulfides, and the characteristics of the mineralization, in which diagenetic sulfates are a sulfur source and Cd enrichment in sphalerite, support the classification of the Sidi Driss and Douahria Pb–Zn deposits as SHMS-Sedex type. Late Miocene extension, comprising rifting dynamics and basalt emplacement, favored a thermally-driven fluid circulation origin for the Sidi Driss and Douahria deposits, enhancing inception of small-scale shallow convection cells. Such sulfide emplacement is significantly different from that of southernmost MVT ore deposits of Tunisia, which are associated with diapirs and are interpreted as the result of a Serravalian–Tortonian gravity-driven fluid circulation event related to late Alpine convergence.

Deep lithospheric structure and the Upper Silesian-Cracovian giant Zn-Pb ore deposits in Poland

Structural study of Palaeozoic folds has been followed by fractal and structural analyses of the fault network in the rock mass underlying the Upper Silesian-Cracovian giant Zn-Pb ore deposits of Mississippi Valley-type. Spatial distribution of the ore occurrences plotted against a background of the results of tectonic study points to determined basement fractures and related Palaeozoic secondary faults as to the zones that enable short-distance flow of mineralising solutions.

Two cytotypes of Kiefferulus tendipediformis (Goetghebuer, 1921) (Diptera, Chironomidae)

The material identified as Kiefferulus tendipediformis on the basis of the larval morphology consisted of two cytogenetically distinct species, which we called cytotype 1 (2n=8) (Bulgaria) and cytotype 2 (2n=6) (Poland). The karyotype and external morphology (larva, pupa and imago - males) of Kiefferulus tendipediformis from pond on mine spoils in the Olkusz region with Zn-Pb ore deposits (Southern Poland) are described. The karyotype of cyto- type 2 (2n =6) (Poland) consists of two metacentric chromosomes (AB and CD) and one submetacentric GEF. The chromosomes AB, CD of both cytotypes are very similar, the chromosome GEF is formed through tandem fusion of two acrocentric chromosomes of cytotype 1 (chromosomes EF and G). The external morphology of the species from Poland is compared with materials of the same species from Bulgaria and Austria. The larvae of Poland and Bulgaria are differed in a number of ultrastructure characters. Pupae and imagoes of K.tendipediformis from Poland are dis- tinguished from those of Austria. The current taxonomic position of the K.tendipediformis in Europe is discussed.

Fluid inclusions in sphalerite as negative crystals: a case study

The crystal morphology of vacuoles of fluid inclusions in some transparent, low-iron and relatively low-temperature sphalerites from the vein and replacement Pb-Zn ore deposits of the Madan ore district, Bulgaria, was studied both by optical microscopy in oriented thin sections and by SEM on open cleavage surfaces. The vacuoles represent negative crystals bounded by faces of d {110}, o {111} and - o {111} forms together with small faces of a {100}, e {210}, n {211}, p {221}, - n {211} and - p {221} forms. Their corners and edges are rounded. The primary inclusions, formed mainly at 200–220 °C, have an isometric, elongated, tubular, spindle-like or acute-angled habit depending on their position and the influence of the growth defects (growth zones, subgrain and sector boundaries, twin planes, etc .). The secondary fluid inclusions, healing fractures in sphalerite crystals mainly at 160–185 °C, are strongly controlled by the thickness and local configuration of the crack surfaces. They are flat, irregular or isometric in shape. It is suggested that the fluid inclusions in the low-T sphalerite usually preserve their initial high-energy and non-equilibrium crystal morphology formed during periods of rapid growth.

Petrogenetic and Metallogenetic Background of the Dajing Cu–Sn–Ag–Pb–Zn Ore Deposit, Inner Mongolia, and Characteristics of the Mineralizing Fluid

Abstract: The Dajing Cu–Sn–Ag–Pb–Zn ore deposit, Inner Mongolia of China, is a fissure‐filling hydrothermal ore deposit that occurs within the Upper Permian Linxi group. No magmatic pluton and volcanic rocks outcrop on the surface of the deposit. Most of ore veins show clear‐cut boundary with country rocks. Wallrock alterations that include silicification, carbonation, chlori–tization, and sericitization are generally weak and occur in the close vicinity of ore veins.Mineralization is divided into three stages: (1) cassiterite–arsenopyrite–quartz stage, (2) sulfide stage, and (3) Pb–Zn–Ag–carbonate stage. These mineralization stages have distinct ranges of homogenization temperatures, 290–350C for Stage 1, 260–320C for Stage 2, and 150–250C for Stage 3. However, salinities for Stages 1, 2, and 3 overlap and range between 2.2 and 10.4 wt % NaCl equivalent. The dD values relative to V‐SMOW of inclusion water from quartz are lower than –88% and centered at –100 to –130%. The δ34S values relative to CDT of sulfide ore minerals and δ13C values relative to PDB of carbonate gangue minerals, vary from –0.3 to +2.6%, and from –7.0 to –2.9%, respectively. Integrated isotopic data point to two major contributions to the mineralizing fluid that include a dominant meteoric‐derived water and the other from hypogene magma for sulfur and carbon species.Analyses of inclusion gas and liquid compositions are performed. The H2O and CO2 are the two most abundant gaseous components, whereas SO42‐ and Cl‐, and Na+, Ca2+, and K+ are the major anions and cations, respectively. A linear trend is shown on the gaseous H2O versus CO2 plot. Phase separation is excluded as cause for the trend on the basis of isotope data and fluid inclusion microthermometry. In addition, a weak wallrock alteration does not support fluid‐rock interaction as an efficient mechanism. Hence, the linear H2O–CO2 trend is interpreted in terms of absorption or dilution of CO2–dominant magmatic vapor by meteoric‐derived water. Cooling effects resulting from dilution may have caused precipitation of ore minerals.Major and trace element compositions of regional granites show a high‐K calc–alkaline characteristics and an arc–affinity. Lead isotopic compositions of galena samples from the Dajing deposit exhibit elevated U/Pb and Th/Pb ratios. These characteristics indicate a common source of supra subduction zone mantle wedge for regional granites and metals from the Dajing deposit.

Metallogenic development of the Krakow terrane suture controlling giant Zn-Pb ore deposits in Poland

Metallogenic development of the Krakow terrane suture controlling giant Zn-Pb ore deposits in Poland

Organic matter in the Upper Silesian (mississippi valley-type) deposits, Poland

Organic matter contained in large amounts in the Upper Silesian Zn-Pb ore deposits has been identified as dopplerite-calcium humate. This humic, amorphous substance was precipitated from humic acids by calcium ion loading. The precipitation of dopplerite was contemporaneous with sulfide deposition at the time of initial and mature karst processes. The hydrothermal karst dissolution supplied calcium ions but the source of humic acids is still conjectural. The geochemical data indicate that the most probable source for the organic matter deposited in the Zn-Pb ores are overlying Triassic Keuper shales containing dispersed humic organic substance.

The PB-Zn ore deposits of San Felipe, Sonora, Mexico: "Detached" mineralization in the Basin And Range Province

La minas de plomo-zinc-plata de San Felipe (Sonora, México) se encuentran en las cercanías de una estructura que presenta las características de un complejo metamórfico ("metamorphic core complex") por lo menos en su parte noreste. Esta estructura está caracterizada por una denudación asociada a la extensión terciaria, la cual afectó el norte de México y el oeste de los Estados Unidos durante el Mioceno. Las unidades del bloque superior, entre las cuales se encuentra el pórfido eocénico superior que contiene en parte los yacimientos de San Felipe, se deslizaron varios kilómetros desde su posición original a lo largo de una falla de despegue: la falla El Amo]. Esta falla corta la zona mineralizada dejando las partes más profundas (skarns) en el bloque inferior, en la parte más alta de la Sierra. Este ejemplo muestra que la distensión debe ser tomada en cuenta en el marco de una exploración minera moderna o en el caso de nuevas búsquedas de reservas en yacimientos conocidos. Se conocen por lo menos dos otros yacimientos en Sonora afectados por procesos similares, un depósito de tungsteno en el flanco oeste de la Sierra de Mazatán, y una parte de la zona oxidada de La Caridad (falla La Caridad). En Arizona, el depósito de San Manuel-Kalamazoo es un ejemplo clásico de un pórfido cuprífero afectado por la extensión terciaria.

Cyclic emersion surfaces and channels within Dinantian limestones hosting the giant Navan Zn-Pb deposit, Ireland

Abstract The Carboniferous succession in the Navan Mine area, which lies near the northern margin of the Dublin Basin, rests unconformably on folded Lower Palaeozoic rocks. The informal stratigraphic nomenclature of the mine is used throughout. Sedimentation began in the late Devonian-early Courceyan with Red Beds reflecting deposition in braided streams and alluvial fans. The overlying Laminated Beds consist of shallow-marine barrier sandstones, tidal-flat/lagoonal mudstones, and sabkha evaporites. The Muddy Limestone is a mud-dominated carbonate sequence reflecting deposition in an open clastic-influenced lagoon. The Pale Beds that follow, and on which attention is focused here, contain at least 44 peritidal and shallow-shelf depositional cycles. The overlying Shaley Pale and Argillaceous Bioclastic Limestones reflect deeper water open-sea conditions. This sequence is truncated by a conspicuous erosion surface overlain by Chadian submarine debris-flows and limestone turbidites. The succession reflects a progressive deepening of the waters as subsidence outpaced sediment accumulation, but emersion surfaces capping cycles indicate that neither deposition nor relative sea-level rise were continuous. Cyclicity and emergence are believed to reflect the interaction of regional subsidence, glacio-eustatic sea-level oscillation, and sediment supply. Emersion surfaces occur in the Laminated Beds and throughout the Pale Beds, and include palaeosols, in situ breccias, pinnacled and hummocky surfaces, and karst-modified topography. Deeply incised channels at four intervals point to larger-scale incision. The lithoclast-bearing conglomerates which they contain indicate extensive emergence nearby. The distribution of these features may be related to the margins of outcrops of Old Red Sandstone and Lower Palaeozoic rocks. The Dinantian limestones in this region host several Zn-Pb ore deposits including Europe’s largest at Navan. The results of this study suggest a relationship to the margins of former emergent carbonate terrains.

Lead isotope study of Zn-Pb ore deposits associated with the Basque-Cantabrian basin and Paleozoic basement, Northern Spain

A total of forty-three galena samples from syngenetic and epigenetic Pb-Zn mineralizations emplaced in the Lower Cretaceous Basque-Cantabrian basin and Paleozoic basement of the Cinco Villas massif in the western Pyrenees, have been analyzed for Pb-isotopic composition. Galena from sedex mineralizations hosted in Carboniferous clastic rocks in the Cinco Villas massif display an homogeneous lead isotopic signature (206Pb/2044Pb ≈ 18.43, 207Pb/204Pb ≈ 15.66, 208Pb/ 204Pb ≈ 38.69) suggesting a single lead reservoir. These values are slightly more radiogenic than lead from other European Hercynian deposits, possibly reflecting the influence of a more evolved upper crustal source. Underlying Paleozoic sediments are proposed as lead source for the Cinco Villas massif ores. Analyses from twenty-six galena samples from the four strata-bound ore districts hosted in Mesozoic rocks reveal the existence of two populations regarding their lead isotopic composition. Galena from the western Santander districts (e.g., Reocin) is characterized by more radiogenic isotope values (206Pb/204Pb ≈ 18.74, 207Pb/204Pb ≈ 15.67, 208Pb/ 204Pb ≈ 38.73) than those from the central and eastern districts (Troya-Legorreta, Central and Western Vizcaya, 206Pb/204Pb ≈ 18.59, 207Pb/204Pb ≈ 15.66, 208Pb/ 204Pb ≈ 38.73). In all districts, the most likely source for these mineralizations was the thick sequence of Lower Cretaceous clastic sediments. The existence of two separate lead isotopic populations could be the result of regional difference in the composition of the basement rocks and the clastic sediments derived of it or different evolution histories. In both sub-basins, isotopic ratios indicate an increase in crustal influence as the age of the ores decreases.

Chemical compositions of tourmaline in the Yindongzi-Tongmugou Pb-Zn deposits, Qinling, China: Implications for hydrothermal ore-forming processes

A microprobe study has been carried out on the chemical composition of tourmaline from the Yindongzi and Tongmugou stratabound Pb-Zn ore deposits, eastern Qinling, China. Tourmaline was analysed from a variety of rock types representative of its various occurrences associated with the ore bodies. All the tourmalines studied here belong to the schorl-dravite series. Most are of hydrothermal origin with Mg > Fe and Na > Ca. Some detrital cores of tourmaline have been recognized from their geometry and chemistry, with Fe > Mg. The chemical trends from core to rim in zoned grains suggest a multi-stage model for the growth of tourmaline and genesis of the ore bodies. The first stage was represented by a more Mg-rich hydrothermal fluid in the submarine hydrothermal system, producing Mg-rich tourmalines by selective replacement of clay-rich sediments close to the sediment-water interface. The second stage was dominated by Fe-rich hydrothermal fluid and resulted in overgrowth of Fe-rich tourmaline rims. This stage also led to the nucleation and growth of new tourmaline crystals and was responsible for the formation of the main massive sulphide orebodies. Finally, a further period of hydrothermal activity or a metamorphic event led to the formation of an additional rim of Mg-rich tourmaline.

Sulphur and lead isotope geochemistry of the Rubiales Zn-Pb ore deposit (NW Spain)

The Rubiales Zn-Pb ore deposit formed by replacement of Lower Cambrian limestones due to hydrothermal fluids that circulated along a fault zone during the Hercynian orogeny. Its lead and sulphur isotopic composition is consistent with that of Cambrian carbonate hosted Zn-Pb deposits of the Hercynian Belt in the CircumMediterranean domain. Sulphur isotope signatures in ore minerals are very uniform, with δ 34 S values of 25.6 ± 0.5 ‰ in sphalerites and 22.6 ± 0.4 ‰ in galenas. These heavy and monotonous values are interpreted in terms of hydrothermal remobilization of pre-existing sulphide mineral occurrences, the sulphur being derived from abiogenic reduction of sulphates equilibrated with Cambrian marine waters. Ore deposition took place at temperatures close to 200°C under reducing conditions and slightly acid to neutral pH; the process was promoted by fluid-carbonate rock interaction. The high 238 U/ 204 Pb and 232 Th/ 204 Pb ratios in galenas support a crustal origin for lead in the ore deposit, seemingly related ultimately to Palaeozoic detritic rocks derived from the erosion of a Precambrian basement. The linear array of lead isotope ratios in the 206 Pb/ 204 Pb- 207 Pb/ 204 Pb and 208 Pb/ 204 Pb- 207 Pb/ 204 Pb diagrams can be interpreted as due to mixing of two different types of lead or selective leaching of the heavier lead isotopes of a primary ore. Sulphur and most of the metals in the deposit may be derived from remobilization of diagenetic, stratabound Zn-Pb mineralizations occurring in Cambrian limestones

Sulphur isotope compositions in the Åmmeberg Zn-Pb ore deposit, south-central Sweden: Genetic implications

The distribution of sulphur isotope compositions in the Ammeberg sulphide ore deposit is discussed. The δ34S values for various sulphides show a complex pattern of fluctuations between isotopic equilibrium and non-equilibrium conditions. This feature as well as the observed variations in the δ34S values of galena and sphalerite are interpreted to have originated from successive pulses of sulphide-forming solutions. On the basis of geological field criteria and sulphur isotope data, the Ammeberg deposit is considered to be a typical distal mineralization, belonging to the volcanic-exhalative group of ore deposits. The banded structure of the ore, the spatial separation of Pb and Zn and the presence of discrete, persistant ore layers probably relate to the type of convective system that created the mineral-forming solutions and to the various processes taking place when the brines were expelled onto the sea floor.