Vein-type Ore Deposits Research Articles

Fluid provenance and genetic type of the Bubin Cu-Pb polymetallic deposit, Kohistan-Ladakh island arc, north Pakistan: Evidence from mineralogy, fluid inclusion and O-H-S-Pb isotopes

The Bubin Cu-Pb polymetallic deposit in Gilgit-Baltistan, Pakistan, is a well-known vein-type ore deposit located in the Kohitan-Ladakh island arc. Due to its significant economic importance as the most important deposit type in the Kohistan-Ladakh island arc, a comprehensive study on its ore genesis, fluids evolution, and genetic classification not only shed new light on our understanding the formation of such polymetallic deposit at a typical intra-oceanic arc, but also of help for the mineral exploration. Here, we present the results from electron probe micro-analyzer, fluid inclusions, Raman spectroscopy, and isotopic studies (O-H-S-Pb) to gain insights into the source of ore-forming fluids and materials, as well as the genetic-type and mechanism of ore precipitation for the Bubin deposit. The mineralization processes were divided into three main stages: Stage I (quartz-pyrite), Stage II (quartz-sulfide), and Stage III (quartz-carbonate). Stage II further comprised two sub-stages: IIa (quartz-chalcopyrite-magnetite) and IIb (quartz-galena-fahlore). The ore-forming fluids exhibited high to moderate temperatures (154–540 °C) and varying salinities (0.35–44.30 wt% NaCl) throughout the stages. Stage I fluids displayed critical behavior with high temperature and low salinity, and their isotopic signatures suggested a magmatic origin. Subsequently, the ore-forming fluids gradually evolved from primary magmatic origin to the mixing of meteoric water, as demonstrated by oxygen and hydrogen isotopic values (δ18Ofluid = -1.34 to 6.29 ‰, δD = -112.4 to −76.1 ‰). The δ34S values (-2.92 to 6.52 ‰) and Pb isotopic ratios (208Pb/204Pb = 39.06 to 40.93, 207Pb/204Pb = 15.72 to 15.99, and 206Pb/204Pb = 19.44 to 20.80) suggested a deep magmatic source for the ore-forming fluid, with metals primarily derived from the upper crust, likely associated with the Ladakh Batholith. Fluid boiling and maxing are the dominant mechanisms for ore mineral precipitation. Additionally, the high to moderate temperature and salinity, presence of solid-bearing and vapor rich inclusions, a Co/Ni ratio > 1, the Ni-As-Co diagram, and O-H-S-Pb isotopic evidence collectively support the classification of the Bubin Cu-Pb polymetallic deposit as an intrusion-related porphyry-style magmatic hydrothermal deposit.

Constraints on the Genesis of Cobalt Deposits: Part I. Theoretical Considerations

Abstract Cobalt is in high demand because of the key role that cobalt-lithium-ion batteries are playing in addressing the issue of global warming, particularly in facilitating the transition from the internal combustion engine to electrically driven vehicles. Here, we review the properties of cobalt and the history of its discovery, briefly describe its mineralogy, and explore the processes that concentrate it to potentially exploitable levels. Economic cobalt deposits owe their origin to the compatible nature of Co2+, its concentration in the mantle in olivine, and its release, after high degrees of partial melting, to komatiitic and (to a lesser extent) basaltic magmas. Primary magmatic deposits, in which Co is subordinate to Ni, develop through the separation of immiscible sulfide liquids from mafic and ultramafic magmas and the very strong partitioning of these metals into the sulfide liquid. We evaluate the factors that concentrate cobalt to economic levels by these processes. Cobalt is also concentrated by aqueous fluids, either at ambient temperature in laterites developed over ultramafic rocks or hydrothermally in sediment-hosted copper deposits and in cobalt-rich vein deposits, where it crystallizes mainly as sulfide and arsenic-bearing minerals, respectively. Using the available thermodynamic data for aqueous Co species, we evaluate cobalt speciation as a function of temperature and show that, whereas it is transported at ambient temperature in most environments as the simple ion (Co2+), it is most mobile in hydrothermal systems as chloride species. Based on thermodynamic data compiled from a variety of sources, we evaluate stability relationships among some of the principal cobalt sulfide and oxide minerals as a function of temperature, pH, fO2, and αH2S and, in conjunction with the aqueous speciation data, determine their solubility. This information is used, in turn, to predict the physicochemical conditions most favorable for cobalt transport and ore formation by hydrothermal fluids. As thermodynamic data are not available for the cobalt arsenide and sulfarsenide minerals that form the vein-type ore deposits, we use chemographic analysis to qualitatively evaluate their stability relationships and predict the physicochemical controls of ore formation. The data and interpretations of processes presented in this paper provide the theoretical basis for a companion paper in this issue in which we develop plausible models for the genesis of the principal cobalt deposit types.

Gamma Ray Spectrometry Method In Detecting The Low Sulfidation Type Epithermal Au+Ag Mineralization (Gümüşhane, Ne Turkey)

Summary The gamma ray spectrometry has been widely used in mineral exploration, geological mapping and environmental radiation monitoring. The Eastern Pontide orogenic belt, which constitutes an important part of the Alpine-Himalayan system, hosts various types of economic mineral deposits of massive sulfide, porphyry copper, skarn, and epithermal vein-type ore deposits. Potassium is generally the most useful pathfinder element for gold mineralization zones. High level K/eTh, K/eU and Efimov F-Parameter (KeU/eTh) anomalies showed the alteration zones transmitting hydrothermal ore solutions to the surface. As a result, the gamma ray spectrometry, which is fast and economics method, might be used for estimation of prospective Au ore zones associated with the K alteration..

Zircon U-Pb geochronology and geochemistry of the intrusions associated with the Jiawula Ag-Pb-Zn deposit in the Great Xing’an Range, NE China and their implications for mineralization

Located in the eastern section of the Central Asian Orogenic Belt, the Jiawula Ag-Pb-Zn deposit is classified as a volcanic to subvolcanic related vein-type ore deposit. New U-Pb zircon geochronology, whole-rock geochemistry, mineral chemistry, and Sr-Nd isotope data are presented for the intrusions in the Jiawula deposit in order to evaluate the timing, petrogenetic type of the granitoid rocks, origin and evolution of magmatism, geodynamics, and to establish its relationship with lead-zinc mineralization. Zircon SHRIMP U-Pb analyses yield weighted mean ages of 150.1±1.8Ma for quartz porphyry, 148.8±2.2Ma for syenite porphyry, and 145.3±1.9Ma for monzonite porphyry, indicating a Late Jurassic (Yanshanian) magmatic event. An earlier magmatic event (Indosinian) occurred during the Late Permian to Early Triassic from ca. 254Ma to ca. 247Ma and is represented by granodiorite (254±2Ma), dacite porphyry (252.9±4.8Ma), and diorite porphyry (278±4.1Ma). Both the Indosinian and Yanshanian igneous rocks are classified as I-type granitoids. The late Jurassic intrusions are highly fractionated and characterized by negative anomalies of Eu, Sr, P, and Ti. The hypabyssal intrusions have initial 87Sr/86Sr values between 0.70458 and 0.70522, and εNd(t) values of −3.4 to −0.2, indicating relatively older crust in Jiawula among more juvenile crust in this area. Magma generation in Jiawula is linked to juvenile lower crustal and slightly enriched mantle sources. The ∼250Ma magmatic episode in Jiawula might be related to the subduction of the Mongol-Okhotsk oceanic plate towards the south beneath the Erguna massif. The ∼150Ma magmatic event occurred after the closure of the Mongol-Okhotsk Ocean followed by the change in subduction direction of the Paleo-Pacific plate. Varying temperature, stronger fractionation and higher oxygen fugacity related to the magmatic-hydrothermal transition caused Pb-Zn mineralization.

High-Resolution Transmission Electron Microscopy (HRTEM) Study of Stacking Irregularity in Fe-Rich Chlorite From Selected Hydrothermal Ore Deposits

AbstractThe structures of Fe-rich chlorite and berthierine and the formation mechanisms of 7 Å–14 Å interstratified minerals were not previously fully understood owing to the difficulties in analyzing them by X-ray diffraction (XRD). The present study characterizes Fe-rich chlorites in quartz veins of epithermal to xenothermal vein-type ore deposits without later structural modifications, based on high-resolution transmission electron microscopy (HRTEM) along with XRD examination and chemical analysis. Samples have a wide range of Fe/(Fe+Mg) ratios from 0.38 to 0.98 and tetrahedral Al substitution for Si from 0.94 to 1.44 atoms per formula unit (apfu). The variation in Fe content nearly parallels the tetrahedral Al content. The formation temperatures estimated by chlorite geothermometry range from 190°C to 320°C. In HRTEM, most of the samples showed interstratification between 7 Å, 14 Å, and/or (in some samples) smectite layers. Chlorites with relatively low Fe contents (Fe/(Fe+Mg) ≈ 0.4) were characterized by mostly 14 Å periodicity with the polytype IIbb. In contrast, interstratification of 7 Å and 14 Å layers predominated with increasing Fe content and the proportion of 7 Å layers exceeds 80% in Fe-rich samples with Fe/(Fe+Mg) > 0.9. The 7 Å component layer approximated Fe-rich berthierine based on the chemical composition. Layer stacking structures in the Fe-rich samples were complex, and characterized by disorder of 7 Å and 14 Å layers, differences in the polarity of the tetrahedral sheets, variations of the slant of the octahedral sheets, and positional disorder between octahedral and tetrahedral sheets involving the hydrogen bonding, as indicated from HRTEM observations along the Yi directions of the phyllosilicates. The complex stacking structures observed in Fe-rich samples suggest that irregularity was controlled by neither the Fe/(Fe+Mg) ratio nor the formation temperature; stacking was controlled by kinetic factors in the process of mineral precipitation under disequilibrium conditions.

Structural geology mapping using PALSAR data in the Bau gold mining district, Sarawak, Malaysia

The application of optical remote sensing data for geological mapping is difficult in the tropical environment. The persistent cloud coverage, dominated vegetation in the landscape and limited bedrock exposures are constraints imposed by the tropical climate. Structural geology investigations that are searching for epithermal or polymetallic vein-type ore deposits can be developed using Synthetic Aperture Radar (SAR) remote sensing data in tropical/sub-tropical regions. The Bau gold mining district in the State of Sarawak, East Malaysia, on the island of Borneo has been selected for this study. The Bau is a gold field similar to Carlin style gold deposits, but gold mineralization at Bau is much more structurally controlled. Geological analyses coupled with the Phased Array type L-band Synthetic Aperture Radar (PALSAR) remote sensing data were used to detect structural elements associated with gold mineralization. The PALSAR data were used to perform lithological-structural mapping of mineralized zones in the study area and surrounding terrain. Structural elements were detected along the SSW to NNE trend of the Tuban fault zone and Tai Parit fault that corresponds to the areas of occurrence of the gold mineralization in the Bau Limestone. Most of quartz-gold bearing veins occur in high-angle faults, fractures and joints within massive units of the Bau Limestone. The results show that four deformation events (D1–D4) in the structures of the Bau district and structurally controlled gold mineralization indicators, including faults, joints and fractures are detectable using PALSAR data at both regional and district scales. The approach used in this study can be more broadly applicable to provide preliminary information for exploration potentially interesting areas of epithermal or polymetallic vein-type mineralization using the PALSAR data in the tropical/sub-tropical regions.

Petrology of ultramafic rocks and Mg-rich carbonate minerals in southeast of Dehshir, Central Iran

The study area is located southeast of Dehshir between the Urumieh-Dokhtar Magmatic Arc and Nain-Baft Ophiolite Belt comprising the Nain, Dehshir, Shahr Babak, and Baft ophiolite complexes. The Dehshir Ophiolitic Complex which obducted in the Late Cretaceous, consists mainly of ultramafic rocks. These remnants of oceanic crust are extensively faulted and fractured. The severe faulting and brecciating of the ophiolite sequence have undergone high-grade alteration and changed it to the tectonic melange. The Dehshir colored melange is bounded to the west by Dehshir fault which is a right-lateral offset of the Nain-Baft suture. In this research, the petrographic studies of the area showed that the ultramafic rocks consist mainly of dunite and harzburgite intruded by diabasic dikes. Syntectonic hydrothermal fluids circulated throughout these rocks. Migration of Mg-rich fluids and hydrothermal brecciating occurred within highly altered and brecciated zones. Magnesite precipitated from hydrothermal solutions and formed the massive, lenticular, and vein-type ore deposits in serpentinized-hosted rocks. Later on, magnesite turned into hydromagnesite due to hydration at the lower depths near the surface. According to the X-ray diffraction and X-ray fluorescence analysis, hydromagnesite is the most dominant and widely occurring Mg-rich carbonate mineral in this area. The main alteration is serpentinization but birbiritization also occurs as a result of interaction between fluids and ultramafic rocks.

Rujevac Sb-Pb-Zn-As polymetallic deposit, Boranja orefield, Western Serbia: native arsenic and arsenic mineralization

Rujevac is a low-temperature hydrothermal polymetallic Sb-Pb-Zn-As vein-type ore deposit, hosted within a volcanogenic-sedimentary zone situated in the Rujevac-Crvene Stene-Brezovica Diabase-Chert Formation (DCF) of the Podrinje Metallogenic District (PMD), Serbia. It is located several kilometers SE from the Boranja contact aureole, which is an integral part of the PMD in Western Serbia. Genetically related to the Tertiary granodioritic magma, the mineral assemblages are characterized by specific features. The mineral association of this deposit consists of sulfides, Pb-Sb(As) sulfosalts, native metals, oxides, hydroxides and gangue minerals. Chemical composition of the ore is very complex, where contents of valuable metals range as follows: Sb (0.17–24.31 wt.%), Zn (0.21–6.29 wt.%), Pb (0.15–6.33 wt.%), As (0.06–1.28 wt.%), Cd (25–747 ppm), Ag (7–408 ppm), Hg (13–473 ppm), and Tl (<1–29 ppm). Electron Probe Microanalyses (EPMA) of native arsenic from both the Rujevac and Stragari deposits showed contents of As up to 98.8 and 97.1 wt.%, with impurity contents of Sb up to 1.3 and 6.6 wt.%, and Tl up to 2 and 1.3 wt.%, respectively. Rhombohedral unit-cell parameters for native arsenic from Rujevac and Stragari deposits amount to: a = 3.760(2), c = 10.555(3) A, V = 129.23(7) A3 and a = 3.763(1), c = 10.560(5) A, V = 129.48(8) A3, respectively. Mineral assemblages, deposition order and genesis of the Rujevac polymetallic deposit were also discussed in detail. Native arsenic mineralization here has been additionally compared with similar well-known global deposits.

Molybdenite Re–Os and muscovite 40Ar/39Ar dating of the Xihuashan tungsten deposit, central Nanling district, South China

The Xihuashan tungsten deposit in the central Nanling region, South China, is an important vein-type ore deposit hosted in Cambrian strata and Mesozoic granitic intrusions. Wolframite and molybdenite are the principal ore minerals. The gangue minerals are mainly quartz and muscovite. Wolframite and molybdenite are products of the first stage hydrothermal activity, whereas muscovite formed dominantly at the second stage. Molybdenite Re–Os and muscovite 40Ar/39Ar dating have been carried out to investigate the age of mineralization. Re–Os isotopic dating for molybdenite associated with wolframite yield a precise, well-constrained isochron age of 157.8±0.9Ma (MSWD=1.5). Ar–Ar isotopic analyses of muscovite yield a plateau age of 152.8±1.6Ma, in agreement with an inverse isochron age of 152.8±1.6Ma, which is ~5mys younger than the Re–Os age. The molybdenite Re–Os age is interpreted as the age of tungsten mineralization. This age coincides well with the zircon U–Pb age of the host granitic intrusion reported previously. The ~5mys difference between molybdenite Re–Os and muscovite 40Ar/39Ar ages probably represents the duration of hydrothermal activity. The results show that the Xihuashan tungsten deposit is one of many important tungsten–tin deposits formed during 150 to 160Ma associated with large-scale lithospheric extension in South China.

Hg-bearing sphalerite from the Rujevac polymetallic ore deposit, Podrinje Metallogenic District, Serbia: Compositional variations and zoning

Rujevac is a low-temperature hydrothermal polymetallic Sb(As)–Pb–Zn vein-type ore deposit, hosted in volcanogenic-sedimentary zone situated in Rujevac-Crvene Stene-Brezovica Diabase-Chert Formation (DCF) of the Podrinje Metallogenic District (PMD), Serbia. The mineralogical composition of the deposit consists of sulfides (stibnite, sphalerite, pyrite, arsenopyrite, galena, realgar and orpiment), sulfosalts (zinkenite, plagionite, robinsonite, twinnite and gratonite), native arsenic, Sb-oxides (valentinite, senarmontite and kermesite), and gangue minerals (quartz, calcite and dolomite). Minerals containing mercury as a major element have not been detected. According to optical features, sphalerite belongs to the cleophane, low Fe content variety (yellowish to colorless). Electron Probe Micro-Analyses (EPMA) of sphalerite revealed wide compositional variations. The Hg content in sphalerite varies between 0.30 and 6.47wt%. The range of other minor elements (Fe and Cd) is highly variable; Mn, Sn, Ge, In, Tl, and As were analyzed, but not detected. Hg-rich zones occur as narrow lamellae and are related to the crystallographic directions of sphalerite. The average values of the EPMA results gave the crystallochemical formula of this sphalerite (Zn0.981, Fe0.007, Cd0.007, Hg0.008)∑1.003S0.997. Strong negative correlations have been determined between ∑Fe+Cd+Hg vs. Zn, and Hg vs. Zn, while these are absent between all other analyzed elements.

Infrared microthermometric and stable isotopic study of fluid inclusions in wolframite at the Xihuashan tungsten deposit, Jiangxi province, China

The Xihuashan tungsten deposit, Jiangxi province, China, is a world-class vein-type ore deposit hosted in Cambrian strata and Mesozoic granitic intrusions. There are two major sets of subparallel ore-bearing quartz veins. The ore mineral assemblage includes wolframite and molybdenite, with minor amounts of arsenopyrite, chalcopyrite, and pyrite. There are only two-phase aqueous-rich inclusions in wolframite but at least three major types of inclusions in quartz: two- or three-phase CO2-rich inclusions, two-phase pure CO2 inclusions and two-phase aqueous inclusions, indicating boiling. Fluid inclusions in wolframite have relatively higher homogenization temperatures and salinities (239–380°C, 3.8–13.7 wt.% NaCl equiv) compared with those in quartz (177–329°C, 0.9–8.1 wt.% NaCl equiv). These distinct differences suggest that those conventional microthermometric data from quartz are not adequate to explain the ore formation process. Enthalpy–salinity plot shows a linear relationship, implying mixing of different sources of fluids. Although boiling occurred during vein-type mineralization, it seems negligible for wolframite deposition. Mixing is the dominant mechanism of wolframite precipitation in Xihuashan. δ34S values of the sulfides range from −1.6 to +0.1‰, indicative of a magmatic source of sulfur. δ18O values of wolframite are relatively homogeneous, ranging from +4.8‰ to +6.3‰. Oxygen isotope modeling of boiling and mixing processes also indicates that mixing of two different fluids was an important mechanism in the precipitation of wolframite.

HYPOGENE Ba-RICH TODOROKITE AND ASSOCIATED NANOMETRIC NATIVE SILVER IN THE SAN MIGUEL TENANGO MINING AREA, ZACATLAN, PUEBLA, MEXICO

The San Miguel Tenango area, in the northern part of the State of Puebla, Mexico, is an old, now-abandoned silver mining district worked intermittently since Colonial times until the 1970s. Ores were high in grade, but had a low metallurgical recovery. We characterize the main ore mineral of this mining area, a Ba-rich manganese oxide with associated native silver, to investigate the cause of the low recovery. The ore deposits of this area consist of veins in Mesozoic limestone and shale, and hydrothermal breccias in early Pliocene dacitic volcanic rocks. Because of the present inaccessibility of the mine workings, only one vein was available for sampling. The ore mineral is Ba-rich todorokite with associated native silver, both occurring as cavity fillings. The vein-type ore deposits are related to adjacent early Pliocene dacitic volcanic rocks consisting of ash-fall tuffs, ash flows, volcanic necks, and a volcanic dome. Transmitted- and reflected-light petrography show that todorokite precipitated during the first stage of mineralization in a wide variety of habits. A second stage of mineralization consists of botryoidal to massive oxides and hydroxides of iron, ending with specular hematite. Filling open spaces in minerals of the second stage are minerals of a third stage consisting of irregular masses of pyrite, chalcopyrite, and pentlandite a few μm across. On the basis of this stage, a hypogene origin is assumed for the previous two stages. An XRD analysis of the vein material revealed the presence of todorokite and an amorphous phase, and probably also a hydrous manganese oxide. Semiquantitative analysis made with SEM–EDS and quantitative analysis with EPMA–SEM showed that the cations in both Mn oxide phases are Ag, Mn, Ba, Ca, Zn, K, Na, Mg, Fe, and Cu, with lesser amounts of Ni, Co, Sb, and Au, the absence of Pb being noteworthy. A TEM study corroborates the presence of todorokite and of an amorphous phase of hydrous manganese oxide, and shows a nanometric crystalline phase that corresponds to manganosite. Also, TEM analyses show that Ag occurs as nanometric particles of native silver adsorbed on the external surfaces of todorokite (not in the tunnels of its structure) and of the amorphous phase. In addition, IR analysis confirms the presence of todorokite. We attribute the low recovery of silver to scavenging of the dissolved silver by todorokite during the metallurgical process.

Tectonic control on vein-type ore deposits in Sapporo-Akaigawa district, southwestern Hokkaido

Tectonic control on vein-type ore deposits in Sapporo-Akaigawa district, southwestern Hokkaido

국내 맥상광체조사를 위한 3차원 전기비저항 모델링자료의 3차원 역산 해석

Department of Energy Systems Engineering, Seoul National University, Seoul 151-744, KoreaAbstact:r Recently as the interest in the development of domestic ore deposits has increased, we can easily find somestudies on exploration geophysics-based ore-deposit survey in literature. Based on the fact that mineralized zone aregenerally more conductive than surrounding media, electrical resistivity survey among several geophysical surveys hasbeen applied to investigate metallic ore deposits. Most of them are grounded on 2-D survey. However, 2-D inversion maylead to some misinterpretation for 3-D geological structures. In this study, we investigate the feasibility of the 3-Delectrical resistivity survey to 3-D vein-type ore deposits. We first simulate 2-D dipole-dipole survey data for survey linesnormal to the strike and 3-D pole-pole survey data, and then perform 3-D inversion. For 3-D ore-body structures, weassume a width-varying dyke, a wedge-shaped, and a fault model. The 3-D inversion results are compared to 2-Dinversion results. By comparing 3-D inversion results for 2-D dipole-dipole survey data to 3-D inversion results for 3-Dpole-pole survey data, we could note that the 2-D dipole-dipole survey data yield better inversion results than the 3-Dpole-pole data, which is due to the main characteristic of the pole-pole array. From these results, we are convinced that ifwe have certain information on the direction of the strike, it would be desirable to apply 2-D dipole-diple survey for thesurvey lines normal to the strike. However, in most cases, we do not have any information on the direction of the strike,because we already developed the ore deposit with the outcrops and the remaining ore deposits are buried under thesurface. In that case, performing 3-D pole-pole electrical resistivity survey would be a reasonable choice to obtain moreaccurate interpretation on ore body structure in spite of low resolution of pole-pole array. 3-D, dipole-dipole array, pole-pole array, electrical resistivity survey, inversion :           ! # $ ' %& * () +,- & / . 0 12 .  34  56 , / 7 89 :; > @ AB * C, E D, FG > : * ,- HI J M KL& , NO  EP R Q 2 ST /  U2 HI .X VW  34 R Q  Y'  RZ, M 1' , Y [ 2\X 9  Y ]^ ; ` _ 1-$ a6 bc 3 ST d* e2 .  fg 3 ST hd ,E 2 ST   2 ST j ;i k HI 56 U lm

Preliminary study on the vein type ore deposits from a viewpoint of fracturing

Preliminary study on the vein type ore deposits from a viewpoint of fracturing

Paleostresses inferred from mesoscale faults in the Late Pliocene Hitoyoshi Formation; implications for the formation of vein-type ore deposits in southern Kyushu

Paleostresses inferred from mesoscale faults in the Late Pliocene Hitoyoshi Formation; implications for the formation of vein-type ore deposits in southern Kyushu

Hydrothermal breccias in vein-type ore deposits: A review of mechanisms, morphology and size distribution

Breccias are among the most widely distributed rock textures found in hydrothermal vein-type deposits. Previous studies have mainly been interested in developing qualitative descriptive approaches, leading to a confusing profusion of terms. Brecciation originates in numerous ways, resulting in highly complex classification systems and frequent misinterpretations of facies. Field observations are difficult to reconcile with physical theories of fragmentation, partly due to the fact that few satisfactory quantitative tools have been developed. A review of the main brecciation processes occurring in hydrothermal vein-type deposits allows for the discrimination between chemical and physical mechanisms, including tectonic comminution, wear abrasion, two types of fluid-assisted brecciation (hydraulic and critical), volume expansion or reduction, impact and collapse. Each of these mechanisms can be distinguished using nonscalar parameters that describe breccia geometry, including fragment morphology, size distribution of the fragments, fabric, and dilation ratio. The first two parameters are especially important because: (1) the morphology of the fragments allows chemical and physical (mechanical) breccias to be distinguished, and (2) the particle size distribution (PSD) is a function of the energy input during breccia formation. The slope of the cumulative PSD (fractal dimension) ranges from high values for high-energy brecciation processes, to low values for low energy processes indicated by an isometric distribution. The evolution of a vein system can be divided into three stages: propagation, wear and dilation. These stages are separated by one threshold of mechanical discontinuity and one of hydraulic continuity. These two thresholds also mark the transition between different types of brecciation. Mineralization occurs during all three stages and may display different textures due to pressure variations. The use of quantitative parameters in fault-related hydrothermal breccias allows a better understanding of the physical parameters related to a vein environment, including structural setting and crustal level, as well as fluid–rock interactions. Recognition of the different breccia types could also be important during the early stages of mineral exploration.

TOURMAL: software package for tourmaline, tourmaline-rich rocks and related ore deposits

TOURMAL is a user-friendly software package developed for editing, storing, calculating and plotting microprobe tourmaline analyses from different geologic environments such as granites and their related aplites and pegmatites, metasomatic and vein type ore deposits, stratabound base metal deposits, gold deposits, and sedimentary and metamorphic rocks. Calculated results, saved in comma delimited ASCII file format, permit the user to search for other applications related to tourmaline compositions. The program prepares 28 binary and seven ternary diagrams. It is written in Quickbasic for IBM PC and compatibles, and runs under DOS and Windows operating systems with a VGA graphic card. This program permits the user to convert standard binary graphs and ternary diagrams into PCX file format for high quality printouts.

Re [sbnd]Os dating of molybdenites from ore deposits in Japan: Implication for the closure temperature of the Re [sbnd]Os system for molybdenite and the cooling history of molybdenum ore deposits

Rhenium and Osmium abundances were determined on molybdenites from eighteen ore deposits in Japan; fifteen vein-type, a skarn-type, a greisen-type, and a pegmatite-type deposit. Re Os ages obtained for molybdenites from northeastern, central, and southwestern Japan are 100–130 Ma, 50–75 Ma, and ca. 10 Ma, respectively, reflecting the ages of regional igneous activities in individual areas. For vein-type ore deposits, Re Os ages for molybdenites agree with Rb Sr whole-rock ages of host granitoids, while they are 3–12 Ma older than K Ar mineral ages of the host rocks. On the other hand, Re Os ages of molybdenites from skarn-, pegmatite-, and greisen-type ore deposits agree with K Ar ages of the host rocks. The comparison of Re Os ages for molybdenites with Rb Sr and K Ar ages of host rocks in vein-type deposits suggests that Re Os closure temperature for vein molybdenite is close to whole-rock Rb Sr closure temperature for host granitic rocks, i.e., roughly estimated to be around 500°C, and higher than K Ar closure temperature for host granodiorites, i.e., 230–370°C, if the thermal history of vein molybdenites is essentially equivalent to that of host rocks. One possible explanation for age discrepancies of 3–12 Ma between Re Os ages for molybdenites and K Ar ages for the wall rocks, observed in vein-type molybdenum deposits, is that later thermal events after formation of molybdenum ores may reset K Ar ages. Hydrothermal alteration might have occurred in such a temperature condition as to disturb K Ar mineral systems in wall rocks and made them younger but not the Re Os system in molybdenite. The other explanation might be that the age discrepancies correspond to a cooling interval from ca. 500 to 300°C of host granitoid. On the other hand, the agreement of Re Os ages of molybdenites and K Ar ages of host rocks in skarn-, pegmatite-, and greisen-type deposits in this study indicates no later disturbance for K Ar system in the wall rock or the rapid cooling of the ore and wall rocks after the formation of molybdenite deposits.

Vein-type ore deposits: Introduction

A vein-type ore deposit is defined here, as: a deposit of ore filling a fissure, or fissures, in rock. This term is non-genetic and is non-restrictive with regard to orientation. The history of vein-type ores illustrates a marked change from their being the major source of most metals, up to the late 19th century, to their being the source of a more limited range of metals today, and in the foreseeable future. Although this volume falls short of a review of all commodities and deposit types, it is justified on the grounds that it contains many new descriptions and represents a time-capsule of the late 20th-century thinking on the geological setting, classification and genesis of vein-type ores.