Carbonate Replacement Deposits Research Articles

The Ciclón - Exploradora epithermal polymetallic ore deposit: An Eocene Cordilleran-type of mineralization in the Domeyko Cordillera, Northern Chile

The Ciclón-Exploradora Project is located in the Exploradora Porphyry Copper District, which corresponds to an old artisanal mining and exploration area 65 km northeast from El Salvador Copper Mine, between 3200 and 4000 m.a.s.l. and inserted within the Eocene-Oligocene metallogenic porphyry belt and Domeyko Cordillera. Exploitation has been discontinuous since the late mid-19th century. It first started with production at the Copper Exploradora Mine, and later for Au–Ag at the Ciclón and San Carlos mines. Nevertheless, after decades of work and exploration the district has great potential for new discoveries.Epithermal polymetallic (Cu–Ag–Zn–Pb–Au) mineralization took place related to the evolution of the Exploradora Plutonic and Porphyry Complex. This Eocene Complex is a composite of dioritic to monzodioritic magmatic intrusions including several intermediate composition Cu–Au and Cu–Mo porphyry centers, mostly emplaced in NNE to NE-oriented corridors. The hosted rocks consists of folded Triassic and Jurassic calcareous sedimentary units partially altered by a kilometric metasomatic envelope that contains skarn mineralization.The complex was mainly emplaced syntectonically along the Sierra Castillo Fault System, which is part of the margin-parallel Domeyko Fault System. These faults together with NE and NW striking transversal faults were active during the Eocene, playing a key role in the emplacement of magmatism and mineralization at the district.The main magmatic phases of the Exploradora Complex record different levels of alteration exposure, mineralization and geochronological ages suggest at least three discrete and continuous episodes of magmatism during ∼4 m.y. (1) An early composite of dioritic to monzodioritic intrusions (38-36 Ma), generally associated with coarse Ca (K) alteration and spatially close to Zn or Fe exoskarn mineralization. (2) An early to inter mineral hypabyssal rocks (36-35 Ma) composed of dacitic to rhyolitic porphyries and aplitic rocks, mostly affected by k-feldspar, propylitic, quartz and argillic alteration, locally with secondary biotite and Cu anomalies. Include quartz monzodiorite porphyries exposing Cu–Au mineralization associated with potassic alteration (biotite-magnetite plus albite) and related quartz-veinlets. (3) CODELCO's Exploradora Cu–Mo mineralization (35-34 Ma) associated with late dacitic and dioritic porphyries, HS-Au mineralization veinlets and a post-mineral diatreme.Polymetallic mineralization occurs at the western part of the district, hosted mainly in sedimentary and intrusive rocks and partially at major intrusion contacts. The Ciclón-Exploradora polymetallic deposit is a 5 km-long NS- and NNW-striking vein-breccia-fault, with mainly sinistral movements, it includes carbonate replacement deposits and dissolution breccia bodies nearby.The tectonic stress field orientation related to the vein-breccia-fault mineralization records subhorizontal NW-trending σ1, SW-trending σ3, and subvertical σ2. Polymetallic hypogene mineralization shows a consistent evolution from low sulfidation conditions to intermediate sulfidation assemblages, spatially related to an early skarn stage characterized by the presence of magnetite, pyrrhotite, Fe-rich sphalerite, developed in calcareous sedimentary rocks. Skarn zonation includes garnet-pyroxene-wollastonite-scapolite minerals. Epithermal polymetallic mineralization shows four main stages. The first and second stages consist of pervasive chlorite followed by chlorite-pyrite veinlets that may or may not contain quartz, and massive pyrite mineralization bodies generally forming euhedral crystals. The second phase ends with a Cu-dominant stage given by chalcopyrite-quartz (±chlorite - sericite – pyrite) and lower contents of Ag-bearing sulfosalts. The third stage is recognized as a polymetallic event characterized by multiple veinlets emplaced both in intrusive and sedimentary rocks where it also forms replacement ore bodies along lithological contacts. It consists of Cd-rich sphalerite, galena, Fe–Mn–Zn carbonates, and minor amounts of chalcopyrite, tennantite-tetrahedrite, and other Ag sulfosalt minerals. Gold is present as native and spectrum minerals with quartz. Main alteration minerals are quartz-kaolinite and minor amounts of sericite. The last stage consists of calcite ± arsenopyrite veinlets crosscutting the previous mineralization. This paragenetic evolution is similar to the one observed in several epithermal porphyry-related polymetallic “Cordilleran” deposits (e.g., Cerro de Pasco, Perú).Crosscutting relationship and exposure of epithermal mineralization, porphyry alteration and magmatism suggests that, in a short period (38–34 Ma), the whole district was exhumed probably several kilometers (3–6 km), related to a compressional to transpressional deformation regime.

Metallogenic model of the Amensif Zn-Pb-Cu-Ag±Au-Bi carbonate replacement deposit (Western High Atlas, Morocco): New litho-structural and mineralogical data

Purpose. In this paper, we discuss the genetic model and emphasize many pending issues on the carbonate replacement textures of the Amensif Zn-Pb-Cu-Ag±Au-Bi deposit (the Western High Atlas, Morocco), the source of metal and the possible contribution of the Azegour granite to this ore genesis. Methods. This study is based on geological mapping, drill core and petrography analysis in combination with ICP-AES, XRD, and SEM data. Findings. The detailed mineralogy consists mainly of sulfides and sulfosalts. The main ore minerals include arsenopyrite, pyrite, sphalerite, chalcopyrite, galena and bismuthinite. Mineral inclusions related to isomorphic sulfosalts are found in galena and/or chalcopyrite. They include matildite, galenobismutite, pavonite, cosalite, schirmerite, krupkaite, ramdohrite, wittichenite, emplectite, luzonite, gustavite, hedleyite, krennerite, wittite, freibergite, tetrahedrite, tennantite and native bismuth. The supergene minerals are anglesite, covellite, malachite, azurite and goethite. In addition, specific replacements are observed between dolomites and sulfides, indicating an interaction between hydrothermal fluid and host rocks. Four ore stages have been identified based on the relationship between mineral phases and ore-forming conditions. The results of this study indicate that Ag and Au precipitation is controlled by the Bi-Te-Pb-S system, while enrichment in Bi, Te and Se sulfosalts and Bi-telluride indicates a magmatic source of the ore-forming fluid. Originality. The study delves into the genetic model of the Amensif Zn-Pb-Cu-Ag±Au-Bi deposit in the Western High Atlas, Moroc-co, with a focus on carbonate replacement textures, while also exploring its classification as either a carbonate replacement deposit or a skarn deposit. Practical implications.Mineral textures are indicators of the replacement process in the Amensif Zn-Pb-Cu-Bi-Ag±Au carbonate replacement deposit (the Western High Atlas, Morocco). The results obtained from this research paper can be used as a powerful tool in mineral exploration of the Western High Atlas.

Metallogeny of the Hunjiang basin, northeastern North China block

The Hunjiang basin in the northeastern North China block is host to a wide range of ore deposit types that are currently exploited by more than 100 past and producing mines. Extensive field and laboratory investigations were conducted to summarize the regional metallogeny, classify the different deposit types, and to place the deposits within a regional geologic and tectonic context. The Archean basement of the basin is host to magnetite deposits that have been affected by high-grade metamorphism. In addition, Proterozoic magmatic Cu-Ni deposit and orogenic Au deposits that are likely of Mesozoic age are located in the metamorphic basement rocks. Polymetallic Co-Cu and Ni-Co-Cu deposits are located in Proterozoic schists within the basin and are of pre- to syn-metamorphic origin. However, most deposits in Hunjiang basin can be related to Mesozoic igneous activity. This includes porphyry Cu and Cu-Mo deposits as well as associated skarns and carbonate replacement deposits. Economically most significant are Au deposits hosted in Proterozoic limestone and dolomite that are located distal to the Mesozoic igneous intrusive centers. This includes the White Mountain deposit near Baishan City, which contains an endowment of more than 50 tonnes Au. There are no known high-sulfidation epithermal deposits within the Hunjiang basin, which is consistent with fluid inclusion evidence demonstrating that emplacement of the porphyry intrusions occurred at significant depth below the paleosurface. Geochronological constraints indicate that Mesozoic igneous activity and associated deposit formation in the Hunjiang basin occurred as a result of Jurassic subduction processes and subsequent extension after slab rollback and lithospheric delamination under the Eastern North China Block in the Cretaceous. Future mineral exploration efforts in the Hunjiang basin should focus on the distal sedimentary rock-hosted Au deposits associated with Mesozoic intrusions, with special emphasis on the northern part of the basin where these deposits occur preferentially at the intersection of extensional faults with a vanished evaporite unit that is distinctly enriched in Fe oxides providing a chemical trap.

Assessment of Sortability Using a Dual-Energy X-ray Transmission System for Studied Sulphide Ore

In hard rock mining, sensor-based sorting can be applied as a pre-concentration method before the material enters the mill. X-ray transmission sensors have been explored in mining since 1972. Sorting ore of acceptable grade and waste material before processing at the mill can reduce the amount of tailings per unit of valuable metal in the mining operation and have many economic benefits. Ore samples used in this paper are from a polymetallic carbonate replacement deposit (gold-silver-lead-zinc sulphide) in Southeast Europe. This paper focuses on how the Dual-Energy X-ray Transmission (DE-XRT) data is generated and used for ore characterization and sortability for this sulphide ore. The method used in the DE-XRT analysis in this project is based on the dual-material decomposition method, which is used in the medical industry for radiology. This technique can distinguish sulphides from non-sulphides. However, the correlation developed between the DE-XRT response and the metal content is lacking. As a result, the DE-XRT response can only classify the material effectively but cannot reliably predict the metal content.

Geology and C-O-S-Pb isotopes of the Fangyangshan Cu-Pb-Zn deposit in the Baoshan block (SW China): Implications for metal source and ore genesis

The Fangyangshan deposit is the first Cu-rich Pb-Zn deposit discovered in the Baoshan block (SW China), the northern continuation of the Sibumasu terrane in mainland SE Asia. The stratabound veined/lensoidal orebodies are hosted in the carbonates and calcareous slates of the Upper Cambrian Shahechang Formation. Based on mineral paragenesis and crosscutting vein relationships, three main mineralization stages (pre-ore (I), syn-ore (II-1 to II-3), and post-ore (III)) were identified at Fangyangshan. Metallic minerals include mainly pyrite, chalcopyrite, sphalerite, and galena, whilst non-metallic minerals include mainly quartz and carbonates (calcite and dolomite). The carbonate δ13CV-PDB and δ18OV-SMOW values vary from the early syn-ore (II-1: −3.67 to −3.57‰, 8.18–8.92‰), middle syn-ore (II-2: −5.88 to −5.26‰, 8.18–10.79‰), late syn-ore (II-3: −2.79 to −2.37‰, 9.97–11.42‰), to post-ore (−3.75‰, 12.79‰) stage. These C-O isotope data suggest that the early ore-forming fluids were predominantly derived from a magmatic source, and the fluids have increasing sedimentary input via wallrock carbonate dissolution. The stages I to II sulfides have consistently high δ34S values (8.24–14.91‰, avg. 11.51‰), which lie between the magmatic- and evaporite-derived δ34S fields, resembling some typical magmatic-related skarn deposits (e.g., Luziyuan, Jinchanghe, Hetaoping and Heiniuwa) in the Baoshan block. This indicates that the Fangyangshan ore sulfur may have been derived from mixture of magmatic-hydrothermal fluids and seawater sulfates (e.g., gypsum) from the local carbonate-evaporite sequences via thermochemical sulfate reduction (TSR). The Fangyangshan sulfides show a clearly linear positive correlation and an upper crustal affinity for their 206Pb/204Pb (18.2984–19.0819), 207Pb/204Pb (15.7731–15.8107), and 208Pb/204Pb (38.6550–39.3092) ratios, which is again similar to many magmatic-related Pb-Zn deposits within the Baoshan block and near the Sino-Burmese border. This also implies a common mixed source of deeper magmatic fluid and upper continental crust for the lead (and also probably other ore metals) in the regional Pb-Zn ore formation. Considering the regional tectono-metallogenic setting, we propose that the Fangyangshan Cu-Pb-Zn mineralization most probably shared a single magmatic-hydrothermal system with the nearby giant Luziyuan distal skarn deposit. These deposits have many similarities with the high-temperature carbonate replacement deposits (CRDs) elsewhere.

Gold ± Copper Endowment and Deposit Diversity in the Western Tethyan Magmatic Belt, Southeast Europe: Implications for Exploration

Abstract Major Au and Cu deposits in the Western Tethyan magmatic belt formed during two main periods of Cretaceous and Cenozoic magmatism. The Cretaceous deposits are dominantly Cu-Au porphyry, high-sulfidation epithermal, and volcanic massive sulfide deposits, whereas in the Cenozoic Cu is significant only in porphyry systems. However, the Cenozoic contains approximately three times greater total Au endowment (for Au deposits >0.5 million ounces), and also has a greater deposit diversity, including porphyry Au-Cu and Au-only deposits, high-, intermediate-, and low-sulfidation epithermal Au systems, and Au-rich carbonate replacement and sediment-hosted styles. The differences in endowment and deposit styles likely reflect regional-scale tectono-magmatic processes as well as local preservation and emplacement levels. The Cu ± Au endowment of the Cretaceous is consistent with typical subduction-related arc environments and generation of calc-alkaline porphyry to high-sulfidation epithermal systems, whereas Au enrichment related to Cenozoic magmatism appears to be related to high-K calc-alkalic to shoshonitic compositions. In many of the Au-rich Cenozoic magmatic belts, there is geochemical evidence for sourcing subcontinental lithospheric mantle that was previously enriched by Cretaceous subduction-related metasomatism. Additional differences in Au endowment may reflect the preservation of shallow-level systems in the Cenozoic, particularly for the Au-rich Miocene porphyry deposits such as Kışladağ and Bierly Vrch and the Apuseni porphyry Au-Cu deposits. However, in both the Cretaceous and Cenozoic, crustal exposure levels vary across the belt and cannot explain all the differences in Cu and Au endowment. A compilation of exploration discovery methods highlights the importance of historic workings in addition to geochemistry and geology as an initial vector, whereas geophysics has had limited involvement in direct discovery, primarily due to its limited application historically. Geologic models for well-understood systems such as porphyry and proximal epithermal systems provide excellent guides for explorers; however, more distal deposits such as Au-rich carbonate replacement deposits and deposits with poorly constrained models such as sedimentary rock-hosted and intermediate-sulfidation deposits are more challenging for exploration.

The Lavrion Pb-Zn-Ag–Rich Vein and Breccia Detachment-Related Deposits (Greece): Involvement of Evaporated Seawater and Meteoric Fluids During Postorogenic Exhumation

AbstractThe formation of ore deposits in the Lavrion Pb-Zn-Ag district was associated with Miocene detachment that accommodated orogenic collapse and exhumation of high-grade nappes across the ductile-brittle transition. This district consists of (1) low-grade porphyry Mo style, (2) Cu-Fe skarn, (3) high-temperature carbonate replacement Pb-Zn-Ag, and (4) vein and breccia Pb-Zn-Ag mineralization. The vein and breccia mineralization locally contains high-grade silver in base metal sulfides that are cemented by fluorite and carbonate gangue. The rare earth element contents of these gangue minerals, chondrite-normalized patterns, and fluid inclusion studies suggest that they precipitated from a low-temperature hydrothermal fluid. Primary and pseudosecondary fluid inclusions in fluorite and calcite are characterized by a wide range of homogenization temperatures (92°–207°C) and salinities of up to 17.1 wt % NaCl equiv. Secondary fluid inclusions only represent <5 vol % of the total fluid trapped. Fluids extracted from inclusions in fluorite have values of δD = –82.1 to –47.7‰ (Vienna-standard mean ocean water [V-SMOW]) and δ18O = –10.4 to –5.1‰ (V-SMOW). These data and low ratios of Cl/Br measured by crush-leach analyses for fluids in fluorite (102–315) and calcite (162–188) are compatible with the ore fluid being the result of mixing of meteoric water with evaporated seawater. These data suggest that fluids leading to the deposition of late Pb-Zn-Ag–rich vein- and breccia-style mineralization in Lavrion were related to circulation of mixed evaporated seawater and meteoric fluids that was enhanced by brittle deformation. This contrasts with the fluids of magmatic origin related to the formation of low-grade porphyry Mo, Cu-Fe skarn, and high-temperature carbonate replacement deposits spatially related to the Plaka granodiorite.

Large-Scale Stable Isotope Alteration Around the Hydrothermal Carbonate-Replacement Cinco de Mayo Zn-Ag Deposit, Mexico

Carbonate-hosted hydrothermal deposits typically show narrow visible mineralogical and textural alteration halos, which inhibit exploration targeting. In contrast, hydrothermal modification of the country rock’s stable isotope composition usually extends far beyond the limited visible alteration. Hence, stable isotope studies should be an effective tool to aid exploration for carbonate-hosted deposits. Here we present new insight into the development of a large stable isotope alteration halo based on 910 O and C isotope analyses of carbonate veins and hydrothermally altered limestone hosting the Cinco de Mayo Pb-Zn-Ag (Au, Cu) carbonate replacement deposit (CRD), in Chihuahua, Mexico. Our results demonstrate that stable isotope alteration is consistent with reactive, magmatic fluid flow into unaltered limestone and represents a powerful tool for the characterization of these hydrothermal ore systems. Synmineralization veins are texturally and isotopically distinct from those formed during pre- and postmineralization diagenesis and fluid flow and show distinct gradients along the direction of mineralizing fluid flow: this appears to be a promising exploration vectoring tool. Downhole variations in wall-rock isotope values reveal aquifers and aquicludes and outline the principal hydrothermal flow paths. Furthermore, wall-rock δ18OVSMOW systematically decreases toward mineralization from ~23‰ to <17‰ over a distance of ~10 km, providing another vectoring tool. The extent of the stable isotope alteration halo likely reflects the overall fluid volume and areal extent of a fossil hydrothermal system, which may be expected to scale with the mineral endowment. This suggests that constraining the size, shape, and degree of isotopic alteration has direct application to mineral exploration by outlining the system and indicating the potential size of a deposit.

Tracing water-rock interaction in carbonate replacement deposits: A SIMS pyrite S-Pb isotope perspective from the Chinese Xinqiao system

Deciphering the sources of metals is a prerequisite to establishing genetic models of ore formation, and is of importance for developing exploration models. For most magmatic-hydrothermal deposits, non-magmatic sourced components (e.g., fluids, sulfur and metals) are suggested to have minor or negligible contributions. On the other hand, there is substantial evidence to indicate that external ore-forming components could be crucial for the mineralization of some magmatic-hydrothermal deposits. Here, we conduct a detailed pyrite sulfur and lead isotope study on the Xinqiao stratabound deposit, South China, with the aim of constraining the contributions of ore-forming components from sedimentary rocks and existing mineralization through water-rock interaction. Traditionally, the source of mineralization at Xinqiao is debated. For example, a Cretaceous magmatic-hydrothermal origin was proposed as the sole source of metals. In sharp contrast, a Carboniferous sedimentary sulfide layer as proto-ore, which was enriched later by the Cretaceous magmatic-hydrothermal fluids, is required in a remobilization model. Crystallized pyrite grains from the stratabound orebody (py1) have a δ34S value of 4.09 ± 1.42 ‰ (2 SD), which is similar to that of pyrite grains from the garnet bearing skarn ore (py3). Colloform pyrite ore, which is composed of fine-grained (∼500 nm) cubic pyrite grains (py2a), has a δ34S value of 0.20 ± 1.14 ‰. The sulfur isotope composition of pyrite grains from the sandstone hosted quartz-pyrite veins is bimodal with δ34S values of 3.28 ± 6.46 ‰ (py4a) and −11.87 ± 5.43 ‰ (py4b). The Pb isotope compositions (206/204Pb ≈ 18.5, 207/204Pb ≈ 15.5) of py1, py4a and py4b are broadly the same as that of K-feldspar from the Cretaceous Jitou diorite, while py2a are more radiogenic (206/204Pb ≈ 21.5, 207/204Pb ≈ 18). Our pyrite S and Pb isotope data show no support for the presence of a Carboniferous sedimentary sulfide layer as proto-ore, but instead suggest that leaching sulfur and metals from Permian shales and an unexposed mineralization through water-rock interaction is a vital mechanism for the mineralization at Xinqiao. In line with previous studies, contributions from the late Permian shales are complementary for the stratabound orebody, and recycling existing Mo-Au rich mineralization is key for the formation of sandstone hosted gold rich pyrite-quartz veins. The existing mineralization is not exposed yet, and should be considered in future mineral exploration. Limited sulfur isotope fractionation between py1, py2 and py3 (0–4 ‰) further indicates a relatively reducing condition during their formation, while significant lower sulfur isotope composition (δ34S = −12 ‰) of py4 could imply an oxidizing condition during its formation. Our study highlights that detailed in-situ sulfur and lead isotope analyses under robust geological and petrographic frameworks can tightly constrain the source of ore-forming components, yield insights into oxygen fugacity during ore formation, and offer clues for future mineral exploration.

Isotopic footprints of the giant Precambrian Caixiashan Zn-Pb mineralization system

Carbonate-replacement Zn-Pb deposits are formed through fluid circulation within carbonate rocks and are an important global source of Zn and Pb. The Caixiashan carbonate-replacement deposit is one of the largest Zn-Pb systems in China. The Mesoproterozoic syn-sedimentary stage (I) of the Caixiashan deposit is characterized by sulfides with negative δ34S values (−25.3 to −8.6‰) generated by organic sulfate reduction, which co-precipitated with the host rocks. The Neoproterozoic main sulfide precipitation stage (II) was caused by thermo sulfide reduction resulting in positive δ34S values (7.9–12.3‰). Carbonates from stage I have δ13CPDB of −1.2 to 2.8‰ and δ18OSMOW of 17.1–24.0‰, similar to those of marine carbonate rocks. Dolomite and calcite from stage II have δ13CPDB ranging from −5.1 to −0.2‰ and δ18OSMOW of 14.1–19.7‰, consistent with dissolution of carbonate rock. In contrast dolomite and calcite from stage III have mantle C-O signatures with the δ13CPDB ranging from −7.5 to 0.4‰ and δ18OSMOW from 5.8 to 13.2‰. C-O isotopic signatures suggest that the original carbonates were dissolved by the acid generated from sulfide precipitation consistent with the sulfide precipitation process. Subsequent precipitation of carbonates created large volumes of dolomite alteration that coated the sulfides and possibly contributed to the preservation of the ore, as dolomite would dissolve more slowly than calcite. Carboniferous magmatism (stage III) resulted in a magmatic overprint on the stage II sulfide. The metal sources of these sulfide ore packets are mainly derived from the Mesoproterozoic carbonate rocks as indicated by the lead isotopes of sulfides and also C-O isotopes of carbonates. The deposit is characterized by a complex paragenesis with multiple overprinting sources of hydrothermal fluids and sulfide over 700 m.y. The syn-sedimentary stage (∼1019 Ma) and main mineralization stage (859–837 Ma) at Caixiashan are chronologically and tectonically associated with the assembly and break-up of the Rodinia supercontinent, whereas the magmatic-hydrothermal modification stage (∼353 Ma) is associated with the closure of the Paleo Asian Ocean during the Early Carboniferous.

THE ISOTOPIC SIGNATURE OF THE MINERALIZING FLUID OF THE LAVRION CARBONATE-REPLACEMENT PB-ZN-AG DISTRICT

The Pb-Zn-Ag carbonate-replacement deposits in the Lavrion district are genetically related to a 7- 10 Ma-old granodiorite, felsic dikes and sills. These deposits are hosted in the Upper and Lower marble and schists of the Cyclades Blueschist unit and occur along the major Legraina detachment fault. Carbonate-replacement orebodies occur as “mantos” and veins, dominated by base metal sulfides and Ag, Bi, Sn, Sb, As, and Pb sulfosalts. Calculated carbon and oxygen isotope compositions of the hydrothermal fluid range from δ13CCO2 of -13.7 to 0.8 per mil and δ18OH2O of 4.2 to 27.4 per mil, at 400º, 350º, 320º, 300º, 250º and 200ºC. These isotopic compositions reveal water-torock ratios ranging from 4.8 to 52.6%, which reflect intense interaction of the ore fluid with the host rock in a water-dominated, transitional closed to open hydrothermal system. The range of δ34SH2S for sulfides in the deposits were from -8.5 to 6.8 per mil, for similar temperatures, whereas for barite-fluorite veins from δ34SH2S of -43.6 to -16.4 per mil, at 200º, 150º and 100ºC. This range implies that there was contribution from a magmatic sulfur component exsolved from the Plaka pluton, as well as contribution from a metasedimentary component. Based on the isotopic signature of sulfur for barite, the ranges from -6.7 to -7.6, comprising an increase in the fluid influx. Isotopic temperatures based on pyrite-galena and sphalerite-pyrite pairs revealed at least three major events of carbonate-replacement ore deposition, (i) at ~ 360º, (ii) 320º-280ºand (iii) 260º-200ºC.

The Lavrion Pb-Zn-Fe-Cu-Ag detachment-related district (Attica, Greece): Structural control on hydrothermal flow and element transfer-deposition

The impact of lithological heterogeneities on deformation, fluid flow and ore deposition is discussed based on the example of the Lavrion low-angle detachment partly accommodating gravitational collapse of the Hellenides orogenic belt in Greece. The Lavrion peninsula is characterised by a multiphase Pb-Zn-Fe-Cu-Ag ore system with a probable pre-concentration before subduction followed by progressive remobilisation and deposition coeval with the development of a low-angle ductile to brittle shear zone. The mylonitic marble below the detachment shear zone is composed of white layers of pure marble alternating with blue layers containing impurities (SiO2, Al2O3, carbonaceous material). Ductile mylonitic deformation is more pervasive in the less competent impure blue marble. We propose that localised deformation in the impure marble is associated with fluid circulation and dolomitisation, which in turn causes an increase in competence of these layers. Mineralised cataclastic zones, crosscutting the mylonitic fabric, are preferentially localised in the more competent dolomitic layers. Oxygen and carbon isotopic signatures of marble invaded by carbonate replacement deposits during ductile to ductile-brittle deformation are consistent with decarbonation coeval with the invasion of magmatic fluids. Mineralised cataclastic zones reflecting brittle deformation evolve from low 13C to low 18O signatures, interpreted as local interaction with carbonaceous material that trends toward the contribution of a surface-derived fluid. These features indicate that the Lavrion area records a complex deposition history influenced by the evolution of fluid reservoirs induced by the thermal and mechanical evolution of the marble nappe stack. Ore remobilisation and deposition associated with the activity of the low-angle detachment is (i) firstly related to the intrusion of the Plaka granodiorite leading to porphyry-type and carbonate replacement mineralisation during ductile-brittle deformation and (ii) then marked by progressive penetration of surface-derived fluids guided by strain localisation in the more competent levels leading to epithermal mineralisation associated with brittle deformation.

An Early Cretaceous carbonate replacement origin for the Xinqiao stratabound massive sulfide deposit, Middle-Lower Yangtze Metallogenic Belt, China

Stratabound massive sulfide deposits are widespread along the Middle-Lower Yangtze Metallogenic Belt (MLYMB) and serve as an important copper producer in China. Two contrasting genetic models have been proposed, interpreting the stratabound massive sulfide deposits as a Carboniferous SEDEX protore overprinted by Cretaceous magmatic-hydrothermal system or an Early Cretaceous carbonate replacement deposit. These two contrasting models have been applied to the Xinqiao stratabound Cu-Au sulfide deposit, which is dominated by massive sulfide ores hosted in marine carbonates of the Carboniferous Chuanshan and Huanglong Formations, with minor Cu-Au skarn ores localized in the contact zone between the Cretaceous diorite Jitou stock and the Carboniferous carbonate rocks. New SIMS zircon U-Pb dating suggests that the Jitou stock formed at 138.5±1.1Ma (2σ, MSWD=0.6). Pyrite Re-Os dating yields an imprecise date of 142±47Ma (2σ, MSWD=7.8). The geochronological data thus constrain the mineralization of the Xinqiao deposit at Early Cretaceous.Fluid inclusions in prograde skarn diopside have homogenization temperatures of 450–600°C and calculated salinities of 13–58wt.% NaCl equiv. Quartz from the stratabound ores and pyrite-quartz vein networks beneath the stratabound ores have homogenization temperatures of 290–360 and 200–300°C, with calculated salinities of 5–12 and 2–10wt.% NaCl equiv., respectively. Quartz from the skarn ores and veins beneath the stratabound ores have δ18O values of 12.32±0.55 (2 SD, n=22) and 15.57±1.92‰ (2 SD, n=60), respectively, corresponding to calculated δ18O values of 6.22±1.59 (2σ) and 6.81±2.76‰ (2σ) for the equilibrated ore-forming fluids. The fluid inclusion and oxygen isotope data thus support a magmatic-hydrothermal origin rather than a SEDEX system for the stratabound ores, with the hydrothermal fluids most likely being derived from the Jitou stock or associated concealed intrusion. Results from this study have broad implications for the genesis and exploration of other stratabound massive sulfide deposits along the MLYMB.

Structural reconstruction and age of an extensionally faulted porphyry molybdenum system at Spruce Mountain, Elko County, Nevada

This study integrates a cross-sectional restoration of normal faults and porphyry-related hydrothermal alteration zones with six new U-Pb zircon dates to constrain the ages of mineralization and large-magnitude Cenozoic extension at Spruce Mountain, northeastern Nevada (USA). Paleozoic sedimentary rocks and sparse rhyolitic intrusive rocks host a porphyry molybdenum deposit dated as ca. 38 Ma that contains associated skarn, carbonate replacements, fissure veins, and jasperoid. At least six crosscutting sets of normal faults with variable dip directions (east, west, and north) and angles ( 60°) are identified at Spruce Mountain, reflecting overprinting phases of extension. Based on the restored cross section, normal faulting at Spruce Mountain resulted in ∼6.9 km (120%) of total extension and ∼35° of net eastward tilting. The first four fault sets, late Eocene (ca. 38 Ma) or older, collectively accommodate most of the total extension (∼5.4 km). Later faults probably were active in the Miocene and Quaternary. All restored faults had initial dips of 45° or greater, and the restored preextensional structure of Spruce Mountain consists of west-vergent folds and gentle westward dips of Paleozoic rocks. Spruce Mountain is classified as a rhyolitic porphyry Mo or Climax-type deposit, with extensive skarn. Eocene rhyolite porphyry dikes associated with porphyry Mo mineralization locally intrude the early generations of normal faults at Spruce Mountain. However, many normal faults also postdate molybdenum mineralization and have partially dismembered the system. Cross-sectional restoration of the postmineralization faulting suggests that the original deposit had an ∼6 km long by ∼3 km deep elliptical pattern with carbonate replacement deposits surrounding skarn.

An assessment of ZTEM and time domain EM results over three mineral deposits

The ZTEM airborne EM system was introduced by Geotech Ltd. into commercial service in 2008. Based on measuring the tipper ratios of AFMAG frequencies, ZTEM provides conductivity information about the earth's near surface that can assist in the exploration for a variety of mineral deposit styles. The results of a surveys over three deposits will be examined; a skarn-style or carbonate replacement deposit in Mexico, a porphyry copper deposit in British Columbia and an epithermal precious-base metals deposit in the Yukon. For each survey, an helicopter time domain EM (HTEM) data set is available to compare with the ZTEM results. Overall, while similarities were noted between the ZTEM and HTEM results, there were also some significant differences that are not totally understood based on available geological information.

Erratum to: Re–Os isotope evidence for mixed source components in carbonate-replacement Pb–Zn–Ag deposits in the Lavrion district, Attica, Greece

The Lavrion ore district contains carbonate-replacement and vein-type Pb–Zn–Ag deposits as well as low-grade porphyry Mo, Cu–Fe skarn, and minor breccia-hosted Pb–Zn–Cu sulfide mineralization. These ore types are spatially related to a Late Miocene granodiorite intrusion (7 to 10 Ma), and various sills and dikes of mafic to felsic composition. Samples of sphalerite and pyrite from the Ilarion carbonate replacement deposit, and galena from Vein 80 (vein-type mineralization) in the Adami deposit show heterogeneous Re–Os values. These values were partially disturbed by hydrothermal activity associated with the formation of hydrothermal veins (e.g., Vein 80). A plot of initial 187Os/188Os versus 1/Oscommon ratios for pyrite and sphalerite from the Ilarion deposit form a mixing line (r2 = 0.78) between high concentration crustal-like and low concentration mantle-like end-members, or two crustal end-members one of which was more radiogenic than the other. Based on the Re–Os systematics and previously published geological and geochemical evidence, the most plausible explanation for the Re–Os isotope data is that ore-forming components were derived from mixed sources, one of which was a radiogenic crustal source from schists and carbonates probably near intrusion centers and the other, intrusive rocks in the district that are less radiogenic. Although the Re and Os concentrations of galena from Vein 80 are above background values they cannot be used as a chronometer. However, the results of the current study suggest that although pyrite, sphalerite, and galena are poor geochronometers in this ore deposit, due to partial open-system behavior, they still yield valuable information on the origin of the source rocks in the formation of bedded replacement and vein mineralization in the Lavrion district.

Ore Deposits and Metallogenesis of Tasmania

Tasmania contains a broad variety of economic mineral deposits, which includes several that have been known for over a century and are still operating today or were worked in the recent past. The Arthur Lineament, a belt of allochthonous amphibolite, carbonate rocks, psammite and pelite in northwest Tasmania hosts the Savage River magnetite deposit, which is now considered to be a Proterozoic carbonate replacement deposit with affinities to Kiruna-style iron-oxide Cu-Au deposits. The allochthon was formed during an early Cambrian collisional event between an east-facing passive margin sequence and an intraoceanic island arc. Post collisional, proximal submarine volcanism at c. 500 Ma in the Mount Read Volcanics followed and associated mineralisation includes world-class deposits. High grade Zn-Pb-Au-Ag-Cu massive sulfide deposits (e.g., Rosebery and Hellyer) were formed from seawater-dominated hydrothermal fluids. Disseminated Cu-Au-Ag deposits of the Mount Lyell field are associated with broad alteration zones that include phyllosilicate assemblages indicative of a component of oxidised magmatic fluid, as does the Henty Au deposit in the north. Orogenic Au is an important deposit style in northeast Tasmania and includes the Tasmania deposit, Australia's largest single Au reef. Largely post-orogenic granitic magmatism (Lower Devonian-Tournaisian) includes an important Sn-W-base metal ± magnetite mineralising event associated with reduced, fractionated granite in northeast and western Tasmania. World class Sn ± Cu sulfide skarn and vein deposits are the product of interpreted magmatic fluids exsolved from these granitic magmas. The highly unusual disseminated Avebury Ni deposit is associated with granite of this type. World class scheelite skarn deposits on King Island lie in the contact aureole of moderately oxidised, unfractionated Tournaisian granodiorite on King Island.

The Geochemistry of Carbonate-Replacement Pb-Zn-Ag Mineralization in the Lavrion District, Attica, Greece: Fluid Inclusion, Stable Isotope, and Rare Earth Element Studies

Strata-bound carbonate-replacement Pb-Zn-Ag deposits in the Lavrion district, Greece, are spatially related to a late Miocene granodiorite intrusion (7–10 Ma) and various sills and dikes of mafic to felsic composition. The Plaka granodiorite contains porphyry molybdenum mineralization and is locally associated with a Ca-Fe skarn. Carbonate-replacement deposits occur predominantly in marbles (Upper and Lower Marble of the Basal unit), Kaesariani schists, and along a major detachment fault that separates the Basal unit from the Upper unit. Orebodies are mainly strata bound carbonate-replacement, although sulfides also occur in veins. The mineralogy of carbonate-replacement deposits is dominated by base metal sulfides and sulfosalts of Ag, Bi, Sn, Sb, As, and Pb, particularly at Plaka and Kamariza. Carbonates are intergrown with earlier formed sulfides and sulfosalts but are more abundant late in the paragenetic sequence with fluorite and barite. Fluid inclusion studies of sphalerite, fluorite, calcite, and quartz in carbonate-replacement deposits suggest that they were deposited from 132° to 365°C from CO2-poor, low- to high-salinity fluids (1–20 wt % NaCl equiv). Carbon and oxygen isotope compositions of calcite ( δ 13C = −15.6 to −1.5‰ and δ 18O = −9.2 to +17.3‰) intergrown with sulfides reflect variable exchange of the ore-bearing fluid with the Upper and Lower Marbles and proximity to the Plaka granodiorite. Post-Archean Australian Shale (PAAS)-normalized rare earth and yttrium patterns of the Upper and Lower Marbles, and calcite intergrown with sulfides show positive Eu and negative Ce anomalies as well as Y/Ho ratios between 40 and 80. Normalized rare earth and yttrium patterns of fluorite also have positive Eu and negative Ce anomalies. Such anomalies for both the carbonates and fluorite reflect the high pH or high f O2 conditions of the late-stage hydrothermal fluids and the likely derivation of calcium from marine carbonates (precursors of the Upper and Lower Marbles). The range of sulfur isotope compositions for sulfides ( δ 34S = −4.9 to +5.3‰, with one outlier of 9.4‰) in carbonate-replacement and vein deposits is due likely to a magmatic sulfur source with a contribution of reduced seawater sulfate. Sulfur isotope compositions of barite from carbonate-replacement range from δ 34S = 17.2 to 23.7 per mil and reflect Miocene seawater sulfate values. If a magmatic source of sulfur is assumed along with an average temperature of 250°C for the ore-forming fluids, as based on fluid inclusion studies, sulfides in carbonate-replacement deposits were deposited at values of log f O2 = −41 to −36 and a pH = 5.8 to 9.1. However, the range of sulfur isotope values does not rule out the possibility that sulfur in sulfides could have been produced by the reduction of seawater sulfate with no contribution from a magmatic source. The carbonate-replacement deposits resemble manto-type sulfide deposits in Mexico, central Colorado, South Korea, Nevada, and northern Greece.

Ages and Sources of Components of Zn-Pb, Cu, Precious Metal, and Platinum Group Element Deposits in the Goodsprings District, Clark County, Nevada

The Goodsprings district, Clark County, Nevada, includes zinc-dominant carbonate replacement deposits of probable late Paleozoic age, and lead-dominant carbonate replacement deposits, copper ± precious metal-platinum group element (PGE) deposits, and gold ± silver deposits that are spatially associated with Late Triassic porphyritic intrusions. The district encompasses ~500 km2 although the distribution of all deposits has been laterally condensed by late Mesozoic crustal contraction. Zinc, Pb, and Cu production from about 90 deposits was ~160,000 metric tons (t) (Zn > Pb >> Cu), 2.1 million ounces (Moz) Ag, 0.09 Moz Au, and small amounts of PGEs—Co, V, Hg, Sb, Ni, Mo, Mn, Ir, and U—were also recovered. Zinc-dominant carbonate replacement deposits (Zn > Pb; Ag ± Cu) resemble Mississippi Valley Type (MVT) Zn-Pb deposits in that they occur in karst and fault breccias in Mississippian limestone where the southern margin of the regional late Paleozoic foreland basin adjoins Proterozoic crystalline rocks of the craton. They consist of calcite, dolomite, sphalerite, and galena with variably positive S isotope compositions ( δ 34S values range from 2.5–13‰), and highly radiogenic Pb isotope compositions (206Pb/204Pb >19), typical of MVT deposits above crystalline Precambrian basement. These deposits may have formed when southward flow of saline fluids, derived from basinal and older sedimentary rocks, encountered thinner strata and pinch-outs against the craton, forcing fluid mixing and mineral precipitation in karst and fault breccias. Lead-dominant carbonate replacement deposits (Pb > Zn, Ag ± Cu ± Au) occur among other deposit types, often near porphyritic intrusions. They generally contain higher concentrations of precious metals than zinc-dominant deposits and relatively abundant iron oxides after pyrite. They share characteristics with copper ± precious metal-PGE and gold ± silver deposits including fine-grained quartz replacement of carbonate minerals in ore breccias and relatively low S and Pb isotope values ( δ 34S values vary from 0–~4‰; 206Pb/204Pb <18.5). Copper ± precious metal-PGE deposits (Cu, Co, Ag, Au, Pd, and Pt) consist of Cu carbonate minerals (after chalcocite and chalcopyrite) and fine-grained quartz that have replaced breccia clasts and margins of fissures in Paleozoic limestones and dolomites near porphyritic intrusions. Gold ± silver deposits occur along contacts and within small-volume stocks and dikes of feldspar porphyry, one textural variety of porphyritic intrusions. Lead isotope compositions of copper ± precious metal-PGE, gold ± silver, and lead-dominant carbonate replacement deposits are similar to those of Mojave crust plutons, indicating derivation of Pb from 1.7 Ga crystalline basement or from Late Proterozoic siliciclastic sedimentary rocks derived from 1.7 Ga crystalline basement. Four texturally and modally distinctive porphyritic intrusions are exposed largely in the central part of the district: feldspar quartz porphyry, plagioclase quartz porphyry, feldspar biotite quartz porphyry, and feldspar porphyry. Intrusions consist of 64 to 70 percent SiO2 and variable K2O/Na2O (0.14–5.33) that reflect proportions of K-feldspar and albite phenocrysts and megacrysts as well as partial alteration to K-mica; quartz and biotite phenocrysts are present in several subtypes. Albite may have formed during emplacement of magma in brine-saturated basinal strata, whereas hydrothermal alteration of matrix, phenocrystic, and megacrystic feldspar and biotite to K-mica, pyrite, and other hydrothermal minerals occurred during and after intrusion emplacement. Small volumes of garnet-diopside-quartz and retrograde epidote-mica-amphibole skarn have replaced carbonate rocks adjacent to one intrusion subtype (feldspar-quartz porphyry), but alteration of carbonate rocks at intrusion contacts elsewhere is inconspicuous. Uranium-lead ages of igneous zircons vary inconsistently from ~ 180 to 230 Ma and are too imprecise to distinguish age differences among intrusion subtypes; most ages are 210 to 225 Ma, yielding a mean of 217 ± 1 Ma. K-Ar and 40Ar/39Ar ages of magmatic (plagioclase, biotite) and hydrothermal (K-mica) minerals span a similar range (183–227 Ma), demonstrating broadly contemporaneous intrusion emplacement and hydrothermal alteration but allowing for multiple Late Triassic magmatic-hydrothermal events. Imprecision and range of isotopic ages may have resulted from burial beneath Mesozoic and Tertiary strata and multiple intrusion of magmas, causing thermal disturbance to Ar systems and Pb loss from zircons in intrusions. Separate late Paleozoic (zinc-dominant carbonate replacement deposits) and Late Triassic (all other deposits) mineralizing events are supported by form, distribution, and host rocks of metal deposits, by hydrothermal mineral assemblages, isotope compositions, metal abundances, and metal diversity, and by small intrusion volumes. These characteristics collectively distinguish the Goodsprings district from larger intrusion related carbonate replacement districts in the western United States. They can be used to evaluate proximity to unexposed porphyritic intrusions associated with PGE and gold ± silver mineralization.

Cinco de Mayo: A new silver, lead, and zinc discovery in northern Mexico

Cinco de Mayo is a carbonate replacement deposit (CRD) style mineral exploration project in the state of Chihuahua, Mexico. Drilling, since November 2007, has confirmed a large zone of high-grade silver, lead, and zinc mineralization. This new, buried mineral deposit is called the Jose Manto (a manto is coherent massive sulphide sheet). The deposit is hosted by the fossiliferous limestone Finlay Formation, with the thickest and most uniform high-grade massive sulphide intersections occurring near its upper and lower contacts. CRD deposits account for roughly 4 billion ounces or 40% of the 10 billion total silver ounces produced in Mexico. They are second only to Mexico's epithermal veins in historic silver production.