Ore-forming Minerals Research Articles

Main minerals of abnormally high-grade ores of the Tomtor deposit (Arctic Siberia)

The Tomtor massif of Paleozoic ultramafic alkaline rocks and carbonatites is located in the northern part of the Sakha Republic (Yakutia). The massif (its total area is ~250 km2) is ~20 km in diameter, with a rounded shape and a concentrically zoned structure. The core of the massif consists of carbonatites surrounded by a discontinuous ring of ultramafic rocks and foidolites. The outer part is composed of alkali and nepheline syenites. All rocks are weathered and covered with eluvium, which is the thickest after carbonatites enriched in phosphates and REE. The weathering profile consists of four layers, from the top: kaolinite-crandallite, siderite, goethite, and francolite. The highest-grade ores are observed in the bedded deposit which fills depressions in “sagging” eluvium. The ores are laminated and cryptogranular, with high Nb, Y, Sc, and REE contents (on average, 4.5% Nb2O5, 7-10% REE2O3, 0.75% Y2O3, and 0.06% Sc2O3). The highest-grade ores are natural Nb and REE concentrates. The total REE content in some layers is >10%. The morphologic features of the highest-grade phosphate ores from the northern part of the Burannyi site were studied. The ore-forming minerals belong to the pyrochlore group, crandallite group (goyazite), and monazite-Ce. The pyrochlore group minerals occur mainly as crystals that were completely replaced by barium-strontium pyrochlore and/or plumbopyrochlore but retained the original faces; also, they occur as numerous conchoidal fragments. The grains of the pyrochlore group minerals sometimes have a zonal structure, with an unaltered pyrochlore core and a reaction rim. Goyazite occurs predominantly as colloform grains. According to SEM and TEM data, monazite occurs in the ores as ~50 nm particles, which cover the outer part of halloysite tubes (800–3000 nm long and 300 nm in diameter) as a dense layer and make up peculiar biomorphic aggregates. The mineralogical data, the occurrence of biomorphic aggregates, and the close association of organic remains with ore minerals suggest that the high-grade ores of the Tomtor deposit, including the Burannyi site, resulted from a hydrothermal-sedimentary process with a presumably important role of bioaccumulation of REE phosphates.

High precision in-situ Pb isotopic analysis of sulfide minerals by femtosecond laser ablation multi-collector inductively coupled plasma mass spectrometry

An in-situ microanalysis of Pb isotopic compositions in sulfide minerals is carried out by using femtosecond laser-ablation multi-collector inductively coupled plasma mass spectrometry (fsLA-MC-ICP-MS). High-temperature-activated carbon was used to filter Hg contained in the carrier gas, which reduced the Hg background signal by 48% and also lowered the detection limit of the analysis. Fractionation and mass discrimination effects existing in the ICP-MS analytical processes were corrected using an internal reference Tl in conjunction with an external reference NIST SRM 610. The proposed method was used to analyze the Pb isotopic compositions of chalcopyrite, pyrite, and sphalerite from the Dulong Sn-Zn-In polymetallic ore district. The results showed that in this ore district, the sulfide minerals and different grains of the same sulfide mineral show a large variation in Pb content up to 1000-fold. The studied pyrites show relatively higher Pb contents and homogeneous Pb isotopic compositions, whereas the sphalerites have low Pb contents but most variable Pb isotopic compositions. It is suggested that the large variation of Pb isotopic composition may reflect a late hydrothermal superimposition on the primary sulfide formation. In addition, radiogenic Pb accumulated by radioactive decay of trace amounts of U over time in the host minerals may also be one of the causes for the large variation range of Pb content and Pb isotopic composition of those low-Pb sphalerites. Chalcopyrite and sphalerite grains with Pb content greater than 10 ppm presented a consistent Pb isotopic distribution, whereas all the sulfide grains with Pb content greater than 100 ppm had consistent Pb isotopic composition within 2s measurement uncertainties. The in-situ analysis of Pb isotopic composition agreed well with the results obtained by conventional chemical methods within 2s measurement uncertainties, indicating that the data obtained by fsLA-MC-ICP-MS are reliable. Additionally, this study indicates that the Pb isotopic composition could truthfully record the source of ore-forming minerals only for sulfide minerals with high Pb content. On the contrary, the Pb isotopic composition of low-Pb sulfide minerals may be affected by trace amounts of U in the host minerals that may lead to a highly radiogenic Pb isotope ratio. Alternatively, it is also possible that late fluid metasomatic overprinting may alter the Pb isotopic compositions.

Introduction to special section: Mining and minerals exploration interpretation

Mineral deposits are found in a variety of geologic settings and ore-forming minerals can have a vast range of physical properties. The search for these deposits is also relatively near-surface thus far. These factors allow for a large number of possible airborne and ground-based techniques to be

Source of Ore-Forming Materials and Mineralization of the Saidu Gold Deposit, Southern Altai, China

Saidu gold deposit, located in back arc basin at south margin of the west Altay Mountain, is orogenic gold deposit. It is strictively controlled by ductile-shear zone, occurring in altered mylonite zone of Mar-kakol giant belt. The δ34S values of pyrite in the gold deposit range from 3.53‰ to 5.88‰; the lead isotopic compositions are fairly constant, with 206Pb/204Pb ranging from 18.010 to 18.359, 207Pb/204Pb ranging from 15.488 to 15.579, and 208Pb/204Pb ranging from 38.1116 to 38.3551. Sulfur and lead isotope studies indicated that ore-forming materials originated from the deep portion, and had close relationship with magmatic activity. The ore materials were obtained from rocks of the lower crust during the orogenic period; the main gold mineralization should have relations with tectonic extention settings of post-collision orogenic.

Geology and Re-Os molybdenite geochronology of the Kurišková U-Mo deposit (Western Carpathians, Slovakia)

*Corr esponding author The Kuriskova U–Mo deposit from the Gemeric Unit of the Western Carpathians (Slovakia) is an example of polygenic deposit whose origin involved several events: endogenous, related to magmatism/volcanism, and exogenous, associated with precipitation from meteoric hydrothermal fluids in repeated tectonically-driven (fold & thrust and shear zones) channel ways penetrating the Permian Huta volcano–sedimentary complex. Sources of the U–Mo mineralization were multiple: (a) molybdenite was derived directly from juvenile hydrothermal fluids related to igneous activity, (b) the U mineralization formed from meteoric fluids circulating through altered and metamorphosed basaltic and rhyolitic volcanics intercalated by clastic sediments (sandstones and mudrocks), which interacted in an arid to humid climate with organic and carbonate substances within Permian basin. The principal ore-forming minerals are uraninite, coffinite, molybdenite and apatite with rare orthobrannerite and powellite. Two basic mineralization forms are present: (a) tabu lar – “stratiform like” and (b) stockwork intraformational and/or dislocation stockworks in shear zones. The Re–Os molybdenite dating confirmed crystallization from igneous source in Late Permian (Lopingian; 257.2 ± 3.0 Ma to 255.6 ± 3.7 Ma) for massive vein mineralization, whereas the superimposed U remobilization within shear zones occurred in the Triassic/Jurassic period. The Kuriskova U–Mo deposit represents a polygenic endo/exogenous hydrothermal deposit of the Permian/Paleo-Alpine age, with metals sourced in Permian volcanosedimentary rocks that were leached by shear zone-related meteoric fluids.

A Tentative Study of Relationship between Mantle Plumes, Supercontinents and Orogenic Gold Deposits

On the basis of predecessors study, this paper found that outbreak frequency of mantle plume is increase, while scale is reduce. The mantle plume provides ore-forming minerals to orogenic gold deposits, as well as affords force to supercontinent formation and decomposition, for the more controls the global tectonic. Supercontinent is the movement of upper crust that could be cause by combine factors of cold and heat mantle plume. Supercontinent supply suitable tectonic environment for orogenic gold deposits. Further, we discuss the relationship between mantle plume, supercontinent and orogenic gold deposit on space and time. With the evolution of the earth, especially the energy loss, the frequency of orogenic gold mineralization is increasing, while the scale is reducing.

COPPER-EXCESS STANNOIDITE AND TENNANTITE-TETRAHEDRITE AS PROXIES FOR HYDROTHERMAL FLUID EVOLUTION IN A ZONED CORDILLERAN BASE METAL DISTRICT, MOROCOCHA, CENTRAL PERU

Porphyry-related Cordilleran polymetallic mineralization in the Morococha district, central Peru, displays a deposit-scale base metal zonation, a common feature observed in many ore deposits of this type. The distinct pattern of zonation consists of Cu-rich ores in the core area and increasingly Zn-, Pb-, and Ag-rich ores in more distal veins and replacement orebodies. We investigated the changing composition of key ore minerals throughout these zones. They are important indicators for the conditions of mineral precipitation and evolving hydrothermal fluid. The mineral species stannoidite Cu8(Fe,Zn)3Sn2S12, vinciennite Cu10Fe4Sn(As,Sb) S16, and tennantite-tetrahedrite have variable Cu content and Fe2+/Fe3+ values between the different base metal zones. Controlled by coupled substitution mechanisms, they show Cu-excess and predominantly ferric Fe compositions in the central areas (Cu and Zn-Cu zones), whereas stoichiometric Cu values and mixed Fe3+ and Fe2+ compositions are typical in the more distal zones (Zn-Pb-Ag and Ag-Pb). These compositional changes are interpreted to reflect decreasing oxidation state of the cooling and evolving fluid and increasing reaction with the host rock toward outer parts of the deposits. Initially high Cu, Fe, and S values in the fluid decrease with precipitation of Cu- and Fe-sulfides. As result of decreasing oxidation state and Fe and Cu values in the fluid, Fe in tennantite-tetrahedrite is increasingly substituted by competing Zn, and Cu by Ag. These data show that compositions of major and even minor ore-forming minerals reflect metal content, oxidation and sulfidation state, and degree of buffering of an evolving hydrothermal fluid by the host rock on a district-scale.

Mineral Paragenesis, Alteration, and Geochemistry of the Two Types of Gold Ore and the Host Rocks from the Carlin-Type Deposits in the Southern Part of the Goldstrike Property, Northern Nevada: Implications for Sources of Ore-Forming Elements, Ore Genesis, and Mineral Exploration

Mineral Paragenesis, Alteration, and Geochemistry of the Two Types of Gold Ore and the Host Rocks from the Carlin-Type Deposits in the Southern Part of the Goldstrike Property, Northern Nevada: Implications for Sources of Ore-Forming Elements, Ore Genesis, and Mineral Exploration

Factors determining origination of gold ore systems in the Russian Far East

Relationships of gold mineralization to deep-seated low-density domains of granitization are considered. The gold mineralization originates in the zones of interaction of these domains with femic rocks established from the results of regional magnetic survey or with thick folded sequences of carbonaceous clay rocks and intercalated members of femic volcanics. The intensity of granitization decreases from continent to ocean, and the ore-forming centers and mineralization are rejuvenated in this direction from the Jurassic-Cretaceous to the Pleistocene, while the productivity of the ore-forming process remains unchanged.

Zircon U-Pb Age and Geochemistry of Granitoids Within Jinla Pb-Zn-Ag Poly-metallic Ore Field Across China and Myanmar Border

Jinla Pb-Zn-Ag poly-metallic ore field across China and Myanma, is tectonically located in the south segment of the Mengtong–Gengma–Ximeng passive continental margin of Proterozoic era-Palaeozoic era, and the eastern margin of the Baoshan–Shantai Massif. Mineralization related granitoids within the ore field include Laochang amphibole admellite, Menglinshan biotite admellite and Nanla K-feldspar granite-porphyry. This paper systematically presents the characteristics of the above granites on their major elements, REE and trace elements (including ore-forming elements) and their isotopic ages determined by zircon SHRIMP dating. The intrinsic connection and genesis of the granites, and the relationships between granites and Pb-Zn-Ag mineralization are discussed. It comes to the conclusions as follows: (1) Among the three types of granites in Jinla ore field, the U-Pb zircon ages for both Laochang porphyraceous amphibole admellite and Menglinshan porphyraceous biotite admellite are (45.41±1) Ma, and Nanla K-feldspar granite porphyry, with a zircon U-Pb age of (43.41±0.78) Ma, formed at the late stage of a syn-collisional mineralization process of Himalayan orogenesis. The magma may have been resulted from partial melting in the crust due to crust and mantle interaction and therefore, is dominated by crustal source materials mixed with some mantle components. Laochang porphyraceous amphibole admellite and Menglinshan porphyraceous biotite admellite contrain significant amount of mantle source materials, whereas Nanla K-feldspar granite porphyry is dominated by crustal materials mixed with minor mantle component. (2) Major and trace elements (including REE and some trace elements (Zr/Hf, Nb/Ta, Rb/Sr, Rb/Ba, K/Rb, (Rb/Yb) N, Sr*, K* and Zr*) suggest that the granitic intrusions in the research area may have formed in locally extensional tectonic environment. Laochang porphyraceous amphibole admellite and Menglinshan porphyraceous biotite admellite may have formed at deep crust during the early stage of magma differentiation. Nanla K-feldspar granite porphyry, on the other hand, may have formed at shallow crust during the late stage of magma differentiation. These three granite intrusions are the products of various stages of magma differentiation during magmatic-tectonic evolution process. (3) Our study on the ore-forming elements in these intrusions suggests that in comparison with granites in China, although Laochang porphyraceous amphibole admellite and Menglinshan porphyraceous biotite admellites are relatively rich in some ore-forming minerals, Nanla K-feldspar granite porphyry has the highest ore-forming potential because, comparing with the other two intrusions, it not only contains more ore-forming minerals, such as W, Cu, Bi, Sb, Mo, Sn, Ag, Pb, Au, etc., the granite is also much richer in F, B, As and other mineralizing elements.

Mineralogical features of uranium ores, large and superlarge deposits of Russia and adjacent countries

The concentration of uranium took place under various ore forming processes (supergene, deep-seated hypergene, hydrothermal) and gave rise to a large number of mineral associations. The author, following the work by Chernikov, Pekov and Minina (1997) distinguishes, on the territory of Russia and adjacent countries, twelve mineralogical types, and several subtypes of uranium ores. Some of these types of ore associations, for instance the beta-uranophane-zeolite, gold-brannerite, molybdenite-brannerite, are not known in other parts of the world. The gold-brannerite, molybdenite-brannerite, pitch-blende-molybdenite ores made up significant and giant deposits. The author explains some physico-chemical conditions in the deep-seated hypergene zone and their role in the formation of large deposits. Also, typomorphic features of ore-forming uranium minerals and associations of large and superlarge deposits are explained. In the complex uranium-vanadium ores (V, Pd , Pt, Au, U) a concentration of noble metals has been established in the near-surface and in the deep-seated oxidized zones. The position of these zones, with a high potential in noble metals, is shown on a vertical section of the Srednija Padma deposit in Karelia, Russia (Fig. 6).

Iron isotope fractionation during hydrothermal ore deposition and alteration

Iron isotopes fractionate during hydrothermal processes. Therefore, the Fe isotope composition of ore-forming minerals characterizes either iron sources or fluid histories. The former potentially serves to distinguish between sedimentary, magmatic or metamorphic iron sources, and the latter allows the reconstruction of precipitation and redox processes. These processes take place during ore formation or alteration. The aim of this contribution is to investigate the suitability of this new isotope method as a probe of ore-related processes. For this purpose 51 samples of iron ores and iron mineral separates from the Schwarzwald region, southwest Germany, were analyzed for their iron isotope composition using multicollector ICP-MS. Further, the ore-forming and ore-altering processes were quantitatively modeled using reaction path calculations. The Schwarzwald mining district hosts mineralizations that formed discontinuously over almost 300 Ma of hydrothermal activity. Primary hematite, siderite and sulfides formed from mixing of meteoric fluids with deeper crustal brines. Later, these minerals were partly dissolved and oxidized, and secondary hematite, goethite and iron arsenates were precipitated. Two types of alteration products formed: (1) primary and high-temperature secondary Fe minerals formed between 120 and 300 °C, and (2) low-temperature secondary Fe minerals formed under supergene conditions (<100 °C). Measured iron isotope compositions are variable and cover a range in δ 56Fe between −2.3‰ and +1.3‰. Primary hematite ( δ 56Fe: −0.5‰ to +0.5‰) precipitated by mixing oxidizing surface waters with a hydrothermal fluid that contained moderately light Fe ( δ 56Fe: −0.5‰) leached from the crystalline basement. Occasional input of CO 2-rich waters resulted in precipitation of isotopically light siderite ( δ 56Fe: −1.4 to −0.7‰). The difference between hematite and siderite is compatible with published Fe isotope fractionation factors. The observed range in isotopic compositions can be accounted for by variable fractions of Fe precipitating from the fluid. Therefore, both fluid processes and mass balance can be inferred from Fe isotopes. Supergene weathering of siderite by oxidizing surface waters led to replacement of isotopically light primary siderite by similarly light secondary hematite and goethite, respectively. Because this replacement entails quantitative transfer of iron from precursor mineral to product, no significant isotope fractionation is produced. Hence, Fe isotopes potentially serve to identify precursors in ore alteration products. Goethites from oolitic sedimentary iron ores were also analyzed. Their compositional range appears to indicate oxidative precipitation from relatively uniform Fe dissolved in coastal water. This comprehensive iron isotope study illustrates the potential of the new technique in deciphering ore formation and alteration processes. Isotope ratios are strongly dependent on and highly characteristic of fluid and precipitation histories. Therefore, they are less suitable to provide information on Fe sources. However, it will be possible to unravel the physico-chemical processes leading to the formation, dissolution and redeposition of ores in great detail.

The Society of Economic Geologists Awards for 2005 R. A. F. Penrose Gold Medal for 2004 Citation of Brian J. Skinner

Mr. President, members and guests: It is a great pleasure to be presenting Brian J. Skinner as the Society of Economic Geologists 2005 Penrose Gold Medalist. To help Brian celebrate his award, we are joined by his wife, Cathy, to whom we extend a very warm welcome. Brian is the 40th recipient of the SEG’s Penrose Gold Medal but it is not the first award he has received from our Society. In 1981 he was awarded the inaugural Silver Medal, and in 2002 he received the Ralph W. Marsden Award. With the award of the 2005 Penrose Gold Medal, he becomes the first person to have received all three of these awards from the SEG. In addition, the Brian J. Skinner Award is named in his honor. This is an exceptional record of recognition and a truly remarkable achievement. The Penrose Medal recognizes a full career in the performance of “unusually original work in the earth sciences.” By any measure, Brian’s career has been full, and the prestigious Penrose Gold Medal is appropriate recognition of his “unusually original work in the earth sciences.” Brian is an unusually original leader in the earth sciences and there would be few here tonight who haven’t been influenced in one way or another by his leadership, either as a researcher, teacher, writer, editor, speaker, or administrator. As a researcher, Brian led teams at the U.S. Geological Survey, and later at Yale University, that gave us new insights into the phase relationships of ore-forming minerals, particularly the sulfosalts and the platinum-group minerals. This research and the findings of his other investigations are reported …

The behavior of trace elements during the chemical evolution of the H2O-, B-, and F-rich granite–pegmatite–hydrothermal system at Ehrenfriedersdorf, Germany: a SXRF study of melt and fluid inclusions

Detailed melt and fluid inclusion studies in quartz hosts from the Variscan Ehrenfriedersdorf complex revealed that ongoing fractional crystallization of the highly evolved H2O-, B-, and F-rich granite magma produced a pegmatite melt, which started to separate into two immiscible phases at about 720°C, 100 MPa. With cooling and further chemical evolution, the immiscibilty field expanded. Two conjugate melts, a peraluminous one and a peralkaline one, coexisted down to temperatures of about 490°C. Additionally, high-salinity brine exsolved throughout the pegmatitic stage, along with low-density vapor. Towards lower temperatures, a hydrothermal system gradually developed. Boiling processes occurred between 450 and 400°C, increasing the salinities of hydrothermal fluids at this stage. Below, the late hydrothermal stage is dominated by low-salinity fluids. Using a combination of synchrotron radiation-induced X-ray fluorescence analysis and Raman spectroscopy, the concentration of trace elements (Mn, Fe, Zn, As, Sb, Rb, Cs, Sr, Zr, Nb, Ta, Ag, Sn, Ta, W, rare earth elements (REE), and Cu) was determined in 52 melt and 8 fluid inclusions that are representative of distinct stages from 720°C down to 380°C. Homogenization temperatures and water contents of both melt and fluid inclusions are used to estimate trapping temperatures, thus revealing the evolutionary stage during the process. Trace elements are partitioned in different proportions between the two pegmatite melts, high-salinity brines and exsolving vapors. Concentrations are strongly shifted by co ncomitant crystallization and precipitation of ore-forming minerals. For example, pegmatite melts at the initial stage (700°C) have about 1,600 ppm of Sn. Concentrations in both melts decrease towards lower temperatures due to the crystallization of cassiterite between 650 and 550°C. Tin is preferentially fractionated into the peralkaline melt by a factor of 2–3. While the last pegmatite melts are low in Sn (64 ppm at 500°C), early hydrothermal fluids become again enriched with about 800 ppm of Sn at the boiling stage. A sudden drop in late hydrothermal fluids (23 ppm of Sn at 370°C) results from precipitation of another cassiterite generation between 400 and 370°C. Zinc concentrations in peraluminous melts are low (some tens of parts per million) and are not correlated with temperature. In coexisting peralkaline melts and high-T brines, they are higher by a factor of 2–3. Zinc continuously increases in hydrothermal fluids (3,000 ppm at 400°C), where the precipitation of sphalerite starts. The main removal of Zn from the fluid system occurs at lower temperatures. Similarly, melt and fluid inclusion concentrations of many other trace elements directly reflect the crystallization and precipitation history of minerals at distinctive temperatures or temperature windows.

Speciation of noble metals and conditions of their concentration in massive sulfide ores of the Urals

The distribution of noble metals has been studied in ores and sulfide concentrates from the Gai, Uchaly, Uzel’ga, Aleksandrinsky, Degtyarsk, and Saf’yanovka deposits. The ores, technological products, and hand-picked monofractions were analyzed with INAA; PGE were determined with kinetic and chromatographic methods after their preliminary chemical separation. The ultraheavy fractions from Au-rich samples were used for examining minerals of noble metals. Phase relations and compositions of ore minerals were studied with an X-ray microprobe and electron microscope equipped with an energy dispersive X-ray analyzer. Gold is associated largely with Fe and Cu minerals (pyrite, chalcopyrite, fahlore) and has been detected as an admixture in Pb, Bi, and Ag tellurides. Pyrite—the major mineral of massive sulfide ores—is the main gold concentrator (up to 20 ppm, ∼1 ppm on average). As follows from the results of rational analysis, the concentration of finely dispersed gold in sulfide ores from the studied deposits ranges from 0.8 to 5.0 ppm, i.e., is less than the bulk Au content in the respective samples (0.93–21.2 ppm). Formation conditions of Au-enriched massive sulfide ores were estimated from the homogenization temperature of fluid inclusions in minerals and on the basis of the electrum-argentite-pyrite-sphalerite and electrum-hessite geothermometers, taking into account the sulfur and tellurium fugacities. The appearance of visible gold and tellurides in ores is caused by recrystallization of their fine-grained intergrowths with ore-forming minerals and, likely, by release of isomorphic admixtures contained in sulfides during epigenetic hydrothermal alteration.

Diagenetic alterations of copper sulfides in modern ore-bearing sediments of the Logatchev-1 hydrothermal field (Mid-Atlantic Ridge 14°45′ N)

Sulfide ore samples recovered by corers from and beyond Orebody 1 in the Logatchev-1 hydrothermal field (Mid-Atlantic Ridge, 14°45′ N) are studied by optical, electron microscopic, X-ray microspectral, and X-ray diffraction methods. The major and ore minerals are identified. Sulfides of the Cu-S system, the major ore-forming minerals in sediments, are investigated in detail. Specific features of their composition, structure, secondary alterations, and distribution in sediments of the Logatchev-1 field are considered. It has been established that sulfide concretions in modern sediments primarily consist of nonstoichiometric minerals of the chalcocite-digenite series, i.e., djurleite (Cu1.96S) and roxbyite (Cu1.75–1.86S). It is assumed that copper sulfides primarily precipitated from hydrothermal solutions as high-temperature hexagonal chalcocite that was replaced after the hydrothermal activity by djurleite, roxbyite, and other nonstoichiometric minerals of the Cu-S system. Based on the comparison of their paragenetic associations with those of copper sulfides in hydrothermal chimneys, the paper discusses constraints of the diagenetic transformation of sulfides in ore-bearing sediments and the halmyrolysis of modern hydrothermal edifices located in contact with seawater. Roxbyite recently discovered in oceanic sediments plays a specific role in these processes.

Ore-forming fluid and mineralization of Caijiaying and Dajing polymetallic ore deposits

Fluid inclusions from the Dajing and Caijiaying deposits have nearly the same homogenization temperature. Correlation between temperature and salinity shows that both Sn- and Cu-bearing fluids Sn and Cu were present in the Dajing deposit but only one kind of fluids continuously evolved in the Caijiaying deposit. Study on rare earth elements (REE) in ancient fluid from the inclusions indicates that the fluid of Sn mineralizing stage in Dajing was derived from remelting magma of the continental crust, and the fluid of Cu-Pb-Zn mineralizing stage in the Dajing deposit and the fluid of Cu-Pb-Zn mineralization in the Caijiaying deposit were derived from the mantle. It is concluded that the Cu-Pb-Zn mineralizations in the Dajing and Caijiaying deposits resulted from the identical tectono-thermal event of magma-fluids induced by Mesozoic tectonic transition and extension in the eastern part of North China Craton.

Carbonatitic Volcanic Genesis of Hetaoqing Fe‐Cu Deposit in Central Yunnan, China

Abstract. The Kunyang rift on western margin of Yangtze Platform is a continental rift, and also a rare Precambrian Fe‐Cu mineralization zone in China. The Wuding‐Lufeng mineralization area in the middle section of the rift is an important part of the zone, and an elliptic‐shaped volcanic collapsed basin, controlled by a ring fracture system with carbonatitic volcanic rocks mainly occurring along the northwestern edge of the basin. The Hetaoqing Fe‐Cu ore deposit at the western side of the basin is hosted in carbonatitic volcanic rocks and pyroclastic sedimentary rocks. The original ore bodies occur as layers, bands and lenses conformable to the host carbonatitic rocks. The ores usually appear as massive, impregnated and granular in carbonatitic rocks, and as brecciform and sandy in pyroclastic sedimentary rocks. Ore‐forming minerals are magnetite, hematite, chalcopy‐rite, bornite, pyrite, carrollite, molybdenite, cobaltite and skinnerite, and secondary minerals limonite, chalcocite, azurite, malachite and tenorite. Gangue minerals are calcite, dolomite, ankerite, common hornblende, arfvedsonite, augite, aegirine‐augite, albite, phlogopite, biotite, chlorite and apatite. Evidences of mineral chemistry, trace elements and isotopic ratios of ores, as well as geological features, suggest that the original ores are igneous in origin. Chemical features of magnetites in the deposit belong to carbonatite type, and are similar to those from the Bayan Obo carbonatites. The ores are rich in iron, titanium, rare earth elements, niobium, tantalum, gold, silver, phosphor and sulfur. These features indicate that the Fe‐Cu deposit associated with volcanic activity in the Wuding‐Lufeng basin is alkali‐carbonatite volcanic type.

The Tellnes ilmenite deposit (Rogaland, South Norway): magnetic and petrofabric evidence for emplacement of a Ti-enriched noritic crystal mush in a fracture zone

The Tellnes ilmenite deposit, a world class titanium deposit, occurs in the Åna–Sira anorthosite (Rogaland anorthosite province, South Norway). It is mainly made up of an ilmenite-rich norite that has been previously interpreted as injected in a crystal mush state, in a weakness zone of the enclosing anorthosite. This emplacement mechanism has produced a faint orientation in the ore due to the flow of the mush. The internal flow structure of the orebody is studied here using the low-field anisotropy of magnetic susceptibility (AMS) method. Partial anhysteretic remanent magnetization (pAARM) indicates that coarse magnetite is the main mineral responsible for the magnetic fabric. Parallelism of the magnetic fabric with the shape-preferred orientation of the ore-forming minerals is checked using image analysis (IA) from oriented sections (intercept method). Interpretation of the AMS data verified by pAARM and IA, provides information on the magmatic foliation and lineation. Emplacement flow of the ilmenite norite crystal mush occurred in the direction of the orebody, parallel to its walls, and with an average SE 18° plunge. The feeder zone was likely situated below a network of veins on the SE end of the orebody. The sickle-shaped outcrop of the deposit suggests a transcurrent, dextral opening of a WNW–ESE-striking weakness zone across the anorthosite pluton.

Can sphalerite be a polarisable mineral? An example from the Century Zn-Pb deposit

While sphalerite is an important ore-forming mineral, the difficulties of exploring for this mineral target due to its low petrophysical contrast with gangue material have been well documented. Fortunately, many large zinc deposits also contain dense and conductive secondary sulphide minerals, which are good targets for standard geophysical tools. The low-grade metamorphic, sediment hosted Century deposit of northwest Queensland represents a style of mineralisation rich in zinc, but with relatively few accessory sulphide minerals. Mineralisation is generally stratiform, consisting of fine-grained laminae of sphalerite, pyrite and galena cross cut by veins of sphalerite and galena in the upper layers of the deposit. Pyrite replaces sphalerite as the main sulphide mineral at the base of the deposit. Of the wide range of techniques applied to detect the deposit, including the gravity, magnetic and electromagnetic methods, only the induced polarisation technique shows a clear anomaly. Conventional wisdom would suggest this induced polarisation anomaly was sourced from galena in the upper part of the deposit or pyrite enrichment in the footwall shales. The authors suggest that sphalerite may be a significant contributor to the observed chargeability response. Further study of the electrical properties of this mineral is required to assess the potential for using induced polarisation as direct targeting tool for zinc-rich orebodies with a low content of secondary sulphides.