Calcite Veinlets Research Articles

Genesis of the Hajibolagh-Zalibolagh Cu-(Ag) intermediate-sulfidation epithermal deposit, Urumieh-Dokhtar magmatic arc, Iran: Evidence from ore geology, fluid inclusions, and stable isotopes

The Hajibolagh-Zalibolagh deposit located northeast of the city of Saveh in the central part of the Urumieh-Dokhtar magmatic arc of Iran, demonstrates vein and breccia vein style copper-(silver) mineralization hosted by Eocene volcano-sedimentary rocks. The main mineralization stage can be divided into four phases, respectively (1) jasperoid + quartz veins, chalcopyrite, and pyrite; (2) quartz veins along with chalcopyrite, bornite, chalcocite, arsenopyrite, and pyrite; (3) quartz-barite veins along with chalcopyrite, bornite, chalcocite and pyrite; and (4) veins of quartz, calcite, hematite, and oligist along with a small number of copper sulfides. The main stages of mineralization are cut by barren post-ore quartz and calcite veinlets. As a result of supergene processes, minerals are oxidized, and malachite, azurite, chrysocolla, chalcocite, covellite, goethite, and hematite are formed, presenting an important exploration guide. The hydrothermal alteration from the center of the vein-veinlets to the outside includes, respectively, silicification, sericitization, intermediate argillic, and propylitic. The average salinity and homogenization temperature (Th) of fluid inclusions is 14.2 wt% NaCl equiv. and 288 °C, respectively. The coexistence of the vapor phase, liquid-rich phase, and halite-bearing fluid inclusions is a sign of boiling in this hydrothermal system, which has contributed to copper saturation. Sulfur isotope values for pyrite, chalcopyrite, chalcocite, and bornite are mainly from –0.16 to 2.98 ‰, indicating a probable magmatic source for sulfur. Boiling, dilution, and mixing are the mechanisms for the ore deposition and facilitated the mineralization. The Hajibolagh-Zalibolagh deposit shows the highest similarity to intermediate-sulfidation epithermal deposits. The best environment for the mineralization and fluid circulation in these epithermal deposits is the intersection of faults with the Eocene volcanic and volcano-sedimentary rocks.

ПРИБРЕЖНАЯ ЭКОСИСТЕМА АПТСКОГО МОРСКОГО БАССЕЙНА РАЙОНА ЕЛШАНО-КУРДЮМСКОГО ПОДНЯТИЯ (САРАТОВСКОЕ ПОВОЛЖЬЕ)

The article presents the results of studies of a number of sections of Lower Cretaceous (Aptian) deposits in the Saratov Right Bank region (settlements Krasnyi Oktyabr’, Doktorovka, Kurdyum and Shirokoe), confined to the Yelshano-Kurdyum uplift. Oryctocenosis combines autochthonous (ichnofossils), subautochthonous (bivalves and gastropods) and allochthonous (ammonites, wood fragments) elements. Sedimentological and mineralogical indicators (ripple marks, desiccation cracks, wedge-shaped structures, cross-bedding, glauconite, and calcite veinlets), as well as fossil remains and features of their taphonomy, allow us to diagnose the coastal ecosystem of the epicontinental sea basin. In the ecosystem format, we see a variety of physico-geographical situations: areas of the bottom which are periodically actively bioturbated and hydrodynamically transformed into mature hardground; zones of active hydrodynamics with the formation of cross-bedding; and zones of subaerial surfaces with the possible development of stick soils. Reconstruction of the paleoecosystem is complicated by the presence of a number of natural facts that have not been unambiguously interpreted, images of which are given in the article. The studied sections are of interest from the standpoint of geoheritage. Selected natural facts are actively involved in the development of a number of geoscientific university museums.

Ore Mineralogy, Fluid Inclusion Geochemistry, and Zircon U-Pb Geochronology of the Nanmingshui Gold Deposit in East Junggar, Xinjiang, Northwest China: Implications for Ore Genesis

The Nanmingshui gold deposit, located in the eastern segment of the Kalamaili gold belt (KGB), is hosted by the sub-greenschist facies rocks of the Lower Carboniferous Jiangbasitao Formation. The genesis of this deposit, however, has been debated for decades because of controversial constraints on the P-T-X conditions and origins of hydrothermal fluid and mineralization age. In this study, we present gold-bearing sulfide compositions, fluid inclusions, H-O isotopes, and the results of hydrothermal zircon U-Pb dating to provide new insights into the genesis of the gold deposit. Three gold mineralization stages are recognized: quartz–pyrite–minor native gold veins (early), quartz–tourmaline–arsenopyrite–pyrite–gold–polymetallic sulfide veins (middle), and quartz–calcite veinlets (late). Gold predominantly occurs as native gold with high fineness ranging from 941 to 944 in sulfides and quartz, and some as solid solutions (Au+) within the lattice of pyrite and arsenopyrite. Three types of primary fluid inclusions are identified in hydrothermal quartz: CO2-H2O (C-type), aqueous (W-type), and pure CO2 (PC-type) inclusions. The early-stage quartz mainly contains C-type and minor W-type inclusions, with total homogenization temperatures (Th) of 220–339 °C, salinities of 0.4–3.7 wt.% NaCl eqv., and bulk densities of 0.66–1.01 g/cm3. All three types of inclusions are observed in the middle-stage quartz, of which the C- and W-type inclusions yield Th values of 190–361 °C, with salinities of 0.4–6.0 wt.% NaCl eqv. and bulk densities of 0.69–0.99 g/cm3. The late-stage quartz contains only W-type inclusions that have lower Th values of 172–287 °C, higher salinities of 1.4–6.9 wt.% NaCl eqv., and bulk densities of 0.79–0.95 g/cm3. Trapping pressures estimated from C-type inclusions in the early and middle stages cluster at 280–340 MPa and 220–310 MPa, respectively, corresponding to metallogenic depths of 10–13 km and 8–11 km. The H-O isotopic compositions (δ18Owater = 1.8–10.9‰, δD = −99 to −62.9‰) and microthermometric data indicate that the ore-forming fluids belong to medium–high-temperature, low-salinity, medium-density, and CO2-rich-H2O-NaCl ± CH4 ± N2 systems, probably originating from metamorphic water. Fluid immiscibility is a crucial mechanism for gold precipitation. Additionally, the U-Pb dating of hydrothermal zircons, from the auriferous quartz–tourmaline vein, yield a weighted mean 206Pb/238U age of 314.6 ± 9.6 Ma. Taking all of the above, the Nanmingshui deposit can be reasonably classed as a typical mesozonal orogenic gold deposit in the KGB, which was formed in a Late Carboniferous tectonic transition from syn-collision between the Jiangjunmiao accretionary complex and Yemaquan arc to post-collision in the East Junggar Orogen. Our results serve to better understand the gold mineralization and genesis of the Late Paleozoic orogenic system in the Kalamaili area, Xinjiang.

Impact of wet-dry cycles on enhanced rock weathering of brucite, wollastonite, serpentinite and kimberlite: Implications for carbon verification

Enhanced rock weathering is a proposed CO2 removal strategy for mitigating climate change; its implementation can be facilitated by improving carbon verification methods. In this study, weathering experiments exposed brucite, wollastonite skarn, serpentinite, and kimberlite residues (Venetia Diamond Mine, South Africa), to wetting and drying cycles (4/day) for 1 yr to elucidate reaction pathways and rates while evaluating carbon verification tools, including mineral quantification, total inorganic carbon (TIC), and stable and radiogenic carbon isotopes. Two primary reaction pathways were identified: A) silicate and hydroxide dissolution leading to carbonate precipitation (desirable), and B) dissolution and reprecipitation of carbonates (undesirable). The kimberlite residues, containing serpentine (19–33 wt%) and calcite (4–5 wt%), experienced variable and minor changes in total inorganic carbon. The δ13C and δ18O values of the carbonate minerals approached those expected for atmospheric-derived CO2 and are best explained by the exchange of carbonate CO2 with atmospheric CO2 (pathway A) as opposed to net CO2 sequestration. In contrast, the reaction of brucite (1.22% to 5.98%) and wollastonite skarn (0.22% to 1.01%) with atmospheric CO2 was substantial, as indicated by the increases in TIC (pathway B) yet decreases in δ13C values were inconsistent with the incorporation of atmospheric CO2 as a result of kinetic isotope fractionation due to carbonation being CO2 supply limited. The pulverized serpentinite experience insufficient carbonation to be detected by TIC. Unweathered (blue ground) and naturally weathered (yellow ground) kimberlite from the Voorspoed Diamond Mine, South Africa were compared to kimberlite residues used in experiments. Yellow ground contained twice the TIC content compared to blue ground whereas quantitative scanning electron microscopy revealed calcite veinlets that are characteristic of secondary mineralization. While the blue and yellow ground samples were essentially radiocarbon dead (0.03 and 0.05 F14C, respectively), substantial modern carbon was incorporated into the kimberlite (up to +0.27 F14C; CO2 exchange), brucite (+0.55 F14C), and wollastonite skarn (+0.53 F14C; CO2 sequestration) powders during weathering experiments. Although stable and radiogenic carbon isotopes have been used to verify the mineralization of atmospheric CO2, these methods are affected by CO2 exchange and kinetic fractionation effects during weathering that can be misleading and, thus, should not be relied on as sole methods for carbon verification.

Geology, mineralization, zircon U-Pb geochronology and Hf isotopes of Serenu porphyry copper prospect, Kerman Cenozoic magmatic arc, southeastern Iran

Serenu porphyry copper prospect is situated 22 km northwest of the Meiduk copper mine, Kerman Cenozoic magmatic arc in southeastern Iran. The study area is characterized by a simple lithology including Eocene volcanic and volcaniclastics, Neogene sediments, and sub-volcanic rocks (Hezar complex) which is intruded by a late Miocene porphyry diorite to quartz-diorite stock that has developed alteration and mineralization in the area. Phyllic, argillic, and propylitic alteration types are well-distributed in the Serenu prospect; potassic alteration is only locally observed. Hypogene mineralization occurs in the Serenu porphyry and the host Eocene volcanic rocks as scattered vein-veinlets, stockworks, and disseminated mineralization related to potassic and phyllic alteration types.The mineralogy and cross-cutting relationships, allow the vein-veinlets to be classified into five groups including (I) magnetite ± quartz, (II) quartz ± magnetite ± chalcopyrite ± pyrite ± chlorite ± anhydrite (III) quartz ± pyrite ± chalcopyrite ± anhydrite, (IV) pyrite, and (V) quartz ± calcite veinlets. Oxide and supergene enriched ores are poorly developed in the area. Zircon U-Pb dating on two samples from the Serenu porphyry provided consistent ages at 9.83 ± 0.4 Ma and 10.2 ± 0.17 Ma (±2σ) indicative of late Miocene emplacement of the intrusion. The zircons are characterized by positive εHf (t) values of 8.52 to 12.27 and TDM of 200–370 Ma and a TCDM of 310–590 Ma indicating that they originated from a juvenile mafic and thickened lower crust and depleted mantle-derived magma.The late Miocene age determined for the Serenu porphyry copper prospect is consistent with the ages reported for many other shallow intrusions related to porphyry-type mineralization in the Kerman belt and further emphasizes the Miocene metallogenic epoch as the preferred time for porphyry Cu-Mo-Au mineralization in this belt, coinciding with a significant stage of continental collision between the Arabian and Iranian plates. The results of this study reveal that the juvenile mafic lower crust together with input from a depleted mantle and older subduction-related magma has a very significant impact on the formation of the Serenu porphyry host magma.

Contribution of Triassic Tectonomagmatic Activity to the Mineralization of Liziyuan Orogenic Gold Deposits, West Qinling Orogenic Belt, China

The Western Qinling orogenic belt (WQOB) is one of the most important prospective gold districts in China, with widely distributed Indosinian intermediate–acidic intrusions. The Liziyuan Au deposit is a representative orogenic deposit in the northern WQOB, hosting several sections spatially associated with igneous rocks. The Au deposit is hosted by meta-sedimentary volcanic rocks of the Cambrian–Ordovician Liziyuan Group and the Tianzishan monzogranite. Two periods, including five stages of mineralization, are recognized in this area: an early metamorphic mineralization period (PI), including quartz–pyrite (Stage I) and banded quartz–polymetallic sulfide (Stage II) veins, and a later magmatic mineralization period (PII) including quartz–K-feldspar–pyrite–molybdenite veins (Stage III), quartz–polymetallic sulfide–chlorite ± calcite veinlets and stockwork (Stage IV), and late calcite–quartz veinlets (Stage V). Geochronological studies indicate a SHRIMP zircon U-Pb age of 236.1 Ma for the Tianzishan monzogranite, and our published ages of ore-bearing diorite porphyrite of the Suishizi section and granite porphyry of the Jiancaowan section being 213 and 212 Ma, respectively. Pyrites formed in association with PI and PII mineralization have well-defined Rb–Sr ages of 220 ± 7.5, 205.8 ± 8.7, and 199 ± 15 Ma, with close temporospatial coupling between mineralization and magmatism. The δ18O and δD values of fluid inclusions in Stage IV auriferous quartz veins range from −0.03‰ to +5.24‰ and −93‰ to −75‰, respectively, suggesting that mineralizing fluid was likely of magmatic origin. Three distinct ranges of δ34S values are identified in the studied sections (i.e., 7.04‰–9.12‰, −4.95‰ to −2.44‰, and 0.10‰–3.08‰), indicating a source containing multiple sulfur isotopes derived from magmatic and metamorphic fluids. The Liziyuan Au deposit is thus likely an orogenic deposit closely related to magmatism. Geochemical characteristics indicate that Tianzishan monzogranite is adakitic and was derived from thickened lower crust during Triassic orogenesis. The ore-bearing diorite porphyrite and granite porphyry formed in a post-collision extensional setting. Together with previous geological and geochemical data, our results indicate that the Liziyuan orogenic Au deposit was formed by early collisional–compressional metamorphism and late post-collision extensional magmatic fluids related to the evolution of the WQOB.

Про значення природних карбонатів у процесах синтезу і генези вуглеводнів у літосфері Землі

The fundamental importance of studies of the processes of synthesis and genesis of hydrocarbons in the Earth's lithosphere has been confirmed and the prospects of the chosen direction for advanced research have been demonstrated, as well as for the thorough development of genetic principles of physical and chemical conditions of the formation of hydrocarbons deposits in various geological minds, focusing on the role of natural carbonate formation in this process. It is shown in this connection that one of the most striking natural phenomena of the Earth’s lithosphere is the obvious manifestations of veinlet-impregnated carbonate mineralization. This has been discussed in detail in the case of some areas of the Ukrainian Carpathians and Pre-Сarpathians, where the original carbonate veinlets of hydrothermal origin with traces of hydrocarbons migration are often happened, but industrial research works is rarely carried out because of their low (as expected) prospects for gas and oil deposits. We pay attention to the areas of development of the calcite veinlets with rare, perfectly faceted crystals of quartz – “Marmarosh diamonds” among the Cretaceous and Paleogene deposits of the South-Western slope of the Carpathians. As a result, supporting materials on the importance of natural carbonates in the processes of synthesis and genesis of hydrocarbons in the Earth’s lithosphere are given. It consists in the revealed previously unknown property of natural carbonates, mainly calcium carbonate, under the action of abiogenic high-thermobaric deep fluid to decompose and be an additional source of carbon with different isotopic compositions in the processes of synthesis and genesis of hydrocarbons: gas, oil, bitumen as well as a carrier of these compounds in time of their migration and conservation in new creations in the deposits of oil and gas-bearing areas and metallogenic provinces: deposits-fields, veins, fluid inclusions, veinlet-impregnated mineralization.

Geology and genesis of the North Narbaghi Cu-Ag deposit in the Urumieh-Dokhtar magmatic arc, Iran: Fluid inclusion and stable isotope constraints

The North Narbaghi Cu-Ag deposit in the central part of the Urumieh-Dokhtar magmatic arc (UDMA) of Iran is hosted by Eocene volcanic sequences and Oligo-Miocene intrusions of arc affiliation. The mineralization can be divided into five stages that are represented by barren hydrothermal breccias, Cu-Fe sulfides cementing in the breccias, sulfosalt and sulfide hydrothermal breccias, barren post-ore quartz veinlets, and barren post-ore calcite veinlets, respectively. The metallic minerals consist of pyrite, chalcopyrite, bornite, sphalerite, and tennantite-tetrahedrite, which are variably associated with gangue minerals including quartz, calcite, and sericite. The upper parts of the ores have been oxidized to form supergene minerals including malachite, azurite, chrysocolla, chalcocite, covellite, hematite, and goethite. The ore-related hydrothermal alteration includes silicification, pyritization, carbonatization, intermediate argillitization, and propylitic alteration. Primary fluid inclusion assemblages in quartz associated with main-stage sulfides and sulfosalts have homogenization temperatures ranging from 184° to 385 °C and calculated salinities between 12.0 and 29.7 wt% NaCl equiv. (avg. 21.4 wt% NaCl equiv.). The coexistence of fluid inclusion assemblages with highly variable volume percentages of vapor phase indicates that boiling commonly occurred in the hydrothermal system, contributing to Cu saturation. Sulfide minerals range in δ34S from −1.5 to 3.7 ‰, indicating a probable magmatic sulfur source. This view is further supported by the carbon and oxygen isotopes of hydrothermal carbonates, with δ13CPDB of −2.2 to −1.5 ‰ and δ18OSMOW between 5.30 and 11.75 ‰. Stable isotope and fluid inclusion data illustrate that boiling of the ore fluid and its mixing with meteoric water facilitated mineralization at the North Narbaghi. We suggest that the North Narbaghi Cu-Ag deposit can be best interpreted as an intermediate-sulfidation epithermal deposit formed due to post-Eocene magmatic-hydrothermal activity. The intersections of post-Eocene subvolcanic rocks with regional faults were the most favorable sites for focusing fluids responsible for epithermal mineralization along the UDMA.

Genesis of carbonatite and associated U–Nb–REE mineralization at Huayangchuan, central China: Insights from mineral paragenesis, chemical and Sr-Nd-C-O isotopic compositons of calcite

The Huayangchuan deposit in the North Qinling alkaline province of Central China is a unique carbonatite-hosted giant U–Nb–REE polymetallic deposit. The mineralization is characterized by the presence of betafite, monazite, and allanite as the main ore minerals, but also exhibit relatively high budgets of heavy rare earth elements (HREE = Gd–Lu and Y). The origin of carbonatites has long been controversial, thus hindering our understanding of the genesis of the deposit. Here, we conducted an in-situ trace elemental, Sr–Nd isotopic, and bulk C–O isotopic analyses of multi-type calcites in the deposit. Two principal types (Cal-I and Cal-II), including three sub-types (Cal-I-1, Cal-I-2 and Cal-I-3) of calcites were identified based on crosscutting relationships and calcite textures. Texturally, Cal-I calcites in carbonatites display cumulates with the grain size decreasing from early coarse- (Cal-I-1) to medium- (Cal-I-2) and late fine-grained (Cal-I-3), whereas Cal-II calcites coexist with zeolite displaying zeolite–calcite veinlets. Geochemically, Cal-I calcites contain relatively high REE(Y) (151–2296 ppm), Sr (4947–9566 ppm) and Na (29–390 ppm) contents, characterized by right- to left-inclined flat distribution patterns [(La/Yb)N = 0.2–4.2] with enrichment of HREE(Y) (136–774 ppm), whereas Cal-II calcites display low REE, Sr and undetectable Na contents, characterized by a right-inclined distribution pattern [(La/Yb)N = 13.5, n = 16]. The U–Nb–REE mineralization, accompanied with intense and extensive fenitization and biotitization, is mainly associated with the Cal-I-3 calcites which show flat to relatively left-inclined flat REE distribution patterns [(La/Yb)N = 0.2–1.0]. Isotopic results show that Cal-I calcites with mantle signatures are primarily igneous in origin, whereas Cal-II are hydrothermal, postdating the U–Nb–REE mineralization. Cal-I calcites (Cal-I-1, Cal-I-2 and Cal-I-3) from mineralized and unmineralized carbonatites, displayed regular changes in REE, Na and Sr contents, but similar trace element distribution patterns and Sr–Nd-C-O isotopic signatures, indicating that these carbonatites originated from the same enriched mantle (EM1) source by low-degree partial melting of HREE-rich carbonated eclogites related to recycled marine sediments. The combination of trace elements and Sr-Nd isotopic composition of calcites further reveals that these carbonatites have undergone highly differentiated evolution. Such differentiation is conducive to the enrichment of ore-forming elements (U–Nb–REE) in the late magmatic–hydrothermal stages owing to extensive ore-forming fluids exsolved from carbonatitic melts. The massive precipitation of the U–Nb–REE minerals from ore-forming hydrothermal fluids may have been triggered by intense fluid–rock reactions indicated by extensive and intense fenitization and biotitization. Therefore, the Huayangchuan carbonatite-related U-Nb-REE deposit may have formed by a combination of processes involving recycled U–Nb–REE–rich marine sediments in the source, differentiation of the produced carbonatitic magmas, and subsequent exsolution of U–Nb–REE–rich fluids that precipitated ore minerals through reactions with wall rocks under the transitional tectonic regime from compression to extension at the end of Late Triassic.

Hydrotermal mineralization hosted by Cambrian sedimentary rocks asevidence of kimberlite-hosting structure, Syuldyukarskoye field, Yakutia

The paper describes diamondiferous kimberlite area within a new Yakutian Syuldyukarskoye fi ld and presents detailed mapping results of ore-hosting shear evidence, veinlet bleaching of redbeds, outcrops of metagrained pyrite, pyrite-calcite and calcite veinlets hosted by Cambrian terrigenous-carbonate rocks where kimberlites occur. Kimberlite localization is shown at fault junction as well as kimberlite long axis combination with west-northwest orehosting shear. These tectonic structures combine with veinlet bleaching halos, those of pyrite-calcite and calcite veinlets, and calcite druses characterized by red photoluminescence and phosphorescence. Red, blue and partially white photoluminescence is caused by manganese concentration in calcites (> 0,1%). Hydrothermal calcite nature is supported by C and O isotope composition variations, which reflect the input of medium temperature formational and meteoric waters, carbon of sedimentary carbonate rocks and deep hydrocarbons. Anomalous Ba, Cr, Ni and La content is recognized in hydrothermal calcites from near-kimberlite environment. Kimberlite position in the southeastern part of endogenous mineralization halos and greater diamond potential of the western kimberlite body, which is larger compared to the eastern one, allow forecasting of new productive bodies.

Colloidal transport and flocculation are the cause of the hyperenrichment of gold in nature

Aqueous complexation has long been considered the only viable means of transporting gold to depositional sites in hydrothermal ore-forming systems. A major weakness of this hypothesis is that it cannot readily explain the formation of ultrahigh-grade gold veins. This is a consequence of the relatively low gold concentrations typical of ore fluids (tens of parts per billion [ppb]) and the fact that these "bonanza" veins can contain weight-percent levels of gold in some epithermal and orogenic deposits. Here, we present direct evidence for a hypothesis that could explain these veins, namely, the transport of the gold as colloidal particles and their flocculation in nanoscale calcite veinlets. These gold-bearing nanoveinlets bear a remarkable resemblance to centimeter-scale ore veins in many hydrothermal gold deposits and give unique insight into the scale invariability of colloidal flocculation in forming hyperenriched gold deposits. Using this evidence, we propose a model for the development of bonanza gold veins in high-grade deposits. We argue that gold transport in these systems is largely mechanical and is the result of exceptionally high degrees of supersaturation that preclude precipitation of gold crystals and instead lead to the formation of colloidal particles, which flocculate and form much larger masses. These flocculated masses aggregate locally, where they are seismically pumped into fractures to locally form veins composed largely of gold. This model explains how bonanza veins may form from fluids containing ppb concentrations of gold and does not require prior encapsulation of colloidal gold particles in silica gel, as proposed by previous studies.

Rapid geochemical imaging of rocks and minerals with handheld laser induced breakdown spectroscopy (LIBS)

Geochemical imaging is a powerful tool for unravelling the complex geological histories of rocks and minerals. However, its applications have until recently been restricted to geological research in a lab environment due to the cost and size of conventional instrumentation, long analysis times, and extensive sample preparation for some methods. Herein we present a rapid, qualitative geochemical imaging method for rocks and minerals using handheld LIBS. Analyses were completed directly on sawed drill core surfaces for a suite of kimberlite-hosted mantle xenoliths (Jericho and Muskox kimberlites, Nunavut, Canada). Semi-automated LIBS spectral processing following a new open-source workflow allows stitching of multiple small-area maps (each approximately 3 × 3 mm that take 2–3 min to complete) to produce cm-scale geochemical images of variably altered mantle xenolith samples (total data acquisition in 1–2 h). Replicate analyses of a ZnAl alloy reference material (NZA-1; CANMET) that were undertaken during standard-sample bracketing suggests that the relative standard deviation (RSD) is typically 15–20% for sum-normalized emission intensities above the estimated background. We demonstrate with open-source machine learning tools how qualitative LIBS spectral data can be converted to Feature-Of-Interest (FOI) maps to distinguish a variety of metasomatic and alteration features (e.g., Cr-diopside, kelyphite rims on pyrope garnet, and calcite veinlets) from the primary mantle mineralogy (e.g., olivine and orthopyroxene). Our results further demonstrate that the resolution of handheld LIBS-based geochemical imaging is sufficient to map veinlets and grain boundaries lined with metasomatic minerals. The LIBS approach is particularly sensitive for mapping the microscale distribution of elements with low atomic number (e.g., Li and Na). These light elements are difficult to detect at low concentrations with other handheld and field-portable technologies, but represent important geochemical tracers of hydrothermal and magmatic processes. Rapid LIBS mapping thus represents an emerging geochemical imaging tool for unravelling the complex geological history of rocks and minerals in the field with minimal to no sample preparation.

Linkage of distal vein–type Au mineralization in carbonate rocks with Cu–Au skarn mineralization in the Fengshan area, Eastern China: Mineralogy and stable isotope geochemistry

Numerous limestone–hosted vein–type Au deposits (12 million tonnes at 5.0 g/t Au) are located peripheral to Cu–Au skarn deposits around the Late Jurassic granodiorite intrusions in the Fengshan area, Middle–Lower Yangtze River metallogenic belt, Eastern China. Both the Cu–Au skarn and distal vein–type Au deposits have a complex mineral assemblage, consisting of base metal sulfides, sulfosalts and Au–Ag–(Tl) telluride minerals. In the Cu–Au skarn deposits, grains of electrum, Au–Ag tellurides (hessite and petzite) coexist with Bi–Te minerals (native bismuth, tetradymite, Phase C, and aikinite), sulfides (chalcopyrite, sphalerite, and galena), occurring as grain aggregates or veinlets. In the distal vein–type Au deposits, fine–grained Au–Ag–Tl tellurides (calaverite, petzite, hessite, and Tl–bearing Au telluride) occur as ore minerals in assemblages of sulfides, and carbonate minerals. The mineralogical Bi–Te signature characterizes the skarn assemblages, while the Te–Tl signature is typical of the distal vein–type Au mineralization.Textural relations and mineral assemblages allow the recognition of five generations of hydrothermal carbonate: (1) Cu sulfides and tellurides–bearing calcite assemblages; (2) sphalerite, galena and tellurides–bearing dolomite assemblages; (3) sericite, quartz and tellurides–bearing carbonate veinlets; (4) realgar and fluorite–bearing carbonate veinlets; (5) pure calcite veinlets. Electron microprobe analysis indicates that the tellurides–bearing, ore–related carbonate contains variable Mn content (up to 80 mol.% MnCO3).The C–O isotope compositions of carbonate from the Cu–Au skarn mineralization, to the carbonate–replacement Pb–Zn and distal vein–type Au mineralization, and to the post–ore, realgar–bearing veinlets in the country rocks display a tendency towards heavier isotopic compositions with time, which could be best interpreted as the effect of fluid–rock interaction between magmatic fluid and the Triassic carbonate host rocks. New S isotope data on sulfate minerals (anhydrite, gypsum, and celestite), and C–O isotopic data suggest a common magmatic fluid source for both skarn and distal vein–type mineralization.

Origin and evolution of hydrothermal fluids in the Marshoun epithermal Pb–Zn–Cu (Ag) deposit, Tarom-Hashtjin metallogenic belt, NW Iran

The Marshoun epithermal Pb–Zn–Cu (Ag) deposit is located in the Tarom–Hashtjin metallogenic belt (THMB), northwest Iran. The epithermal base metal veins are mainly hosted in Eocene volcanic and volcaniclastic rocks of the Karaj Formation, and late Eocene pyroxene quartz monzodiorite. The mineralization process can be divided into five stages: (1) quartz-chalcopyrite-pyrite veins and breccias, (2) quartz (calcite)-sphalerite-galena ± chalcopyrite ± pyrite veins and breccias, (3) barren post-ore quartz veinlets, (4) barren post-ore calcite veinlets, and (5) supergene mineral assemblages. The primary metallic minerals are pyrite, chalcopyrite, sphalerite, and galena; gangue minerals are mainly quartz, calcite, sericite, and chlorite. The main wall-rock alteration is silicification, intermediate argillic, carbonate, and propylitic alteration. Microthermometric measurements of primary LV fluid inclusion assemblages in quartz and sphalerite indicate that the veins were mainly formed at temperatures between 173 and 285 °C from fluids with salinities between 3.4 and 6.3 wt% NaCl equiv. Coexisting LV, VL, and V inclusions in quartz and sphalerite provide evidence for boiling in ore-stage breccia and veins. Additionally, the occurrence of bladed calcite as well as plumose and colloform/crustiform banded quartz in the ore zones and the presence of hydrothermal breccias are consistent with boiling. Obtained oxygen and sulfur isotope compositions (δ18Owater = +9.2‰ to +1.5‰; δ34SH2S = –10.0‰ to –5.7‰) indicate there was a major contribution from a magmatic component to metallogenesis. The fluid inclusion and stable isotope data indicate that fluid boiling and mixing facilitated hydrothermal alteration and mineralization at Marshoun. The Marshoun deposit is interpreted as an intermediate-sulfidation style of epithermal mineralization. Our data suggest that the epithermal mineralization in the THMB are related to late Eocene (ca. 36–37 Ma) shallow magmatic–hydrothermal activity. The altered Eocene volcanic-subvolcanic rocks, particularly at the intersection of subvolcanic rocks with faults were the most favorable locus for exploration targeting of epithermal ores at THMB.

Geological, geochronological and geochemical characteristics and genesis of the Arqiale skarn Zn-Pb deposit, Western Tianshan, Northwest China

The Arqiale deposit, located in the southern Yili Block of Western Tianshan, Xinjiang, China, is a newly discovered large Zn-Pb deposit with a resource of approximately 10 million tons ore grading 9.65% Zn+Pb, and a certain amount of Cu and Ag. The Zn-Pb orebodies are tabular and lentoid in shape, developed along SW-striking and NW-dipping interlayer structures between the Lower Carboniferous Akeshake (mainly carbonate rocks) and Dahalajunshan (mainly volcanic rocks) formations.Garnet and pyroxene-rich skarn, formed in the early (prograde) stage of skarnization, occurs only locally as lenses within skarn bodies enriched in actinolite, tremolite, ilvaite, biotite, epidote, chlorite, calcite, quartz and fluorite, which were formed in the retrograde stage. Metallic minerals comprise sphalerite, galena, chalcopyrite, pyrite, and hematite. They mainly occur as disseminations, patches and massive ores, replacing retrograde skarn minerals and crosscut by later stage quartz and calcite veinlets. There is a general trend of increasing Cu contents and decreasing Zn/Pb ratios from the upper and south portion to the lower and north portion of the orebody.Rb-Sr dating of seven sphalerite samples yielded an isochron age of 339.5 ± 2.7 Ma, which is almost identical to the 341.8 ± 2.5 Ma age obtained from Sm-Nd dating of eight actinolite samples. Furthermore, zircon U-Pb dating yielded an age of 343 ± 6 Ma for a gabbro-diorite stock that is located about 600 m south of the Zn-Pb orebody. The age data indicate that the mineralization and retrograde skarnization were contemporaneous, and they are likely related to a magmatic intrusion of similar age which may be linked to the gabbro-diorite stock. Thus, although the direct causative intrusion has not been identified, the Arqiale deposit can be classified as a distal skarn deposit. The δ34SV-CDT values of 26 ore sulfide samples range from −7.1‰ to +1.3‰ with an average of −1.5‰. The 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios of 25 ore sulfide samples range from 18.266 to 18.880, 15.577 to 15.668 and 38.068 to 38.720, respectively, which are similar to the Early Carboniferous intrusions of the Wusun Range and partly overlap with the volcanic rocks of the Dahalajunshan Formation, and are different from the carbonate rocks of the Akeshake Formation. Based on these data, we propose that the Arqiale deposit formed from magmatic-hydrothermal fluids emanated from a concealed magmatic intrusion which may be located beneath the northern and deep part of the deposit. Much of the metals and sulfur may have been derived from the magmatic intrusions, although some of them may have also been extracted from the volcanic rocks underlying the deposit. The results of this study indicate that there is a great potential of finding more skarn Zn-Pb mineralization in Western Tianshan, where numerous Early Carboniferous arc-related intrusions with similar ages as the Arqiale deposit, in relation to the subduction of the Southern Tianshan Oceanic plate underneath the Yili-Central Tianshan Block, were emplaced into or beneath carbonate rocks.

C and O stable isotopes and rare earth elements in the Devonian carbonate host rock of the Pivehzhan iron deposit, NE Iran

The Pivehzhan iron deposit is located at about 80km southwest of Mashhad, NE Iran. They occur within the Devonian carbonates as lenticular and massive bodies, as well as veinlets of magnetite and iron sulphides, transformed to goethite and haematite by weathering process. The hydrothermal calcite is the most important gangue mineral, which is observed in the form of veins/veinlets and open-space filling. The iron ores are accompanied by some minor elements such as Mn, Ti, Cr, and V and negligible amounts of Co and Ni. The distribution pattern of Rare Earth Elements (REEs) normalized to Post Archean Australian Shale (PAAS), which is characterized by the upward convex, as well as the positive Eu anomalies indicate the activity of reduced and acidic hydrothermal fluids. The negative Ce anomalies of host carbonates, although slight, point to the dominance of anoxic conditions during interaction with hydrothermal fluids. The hydrothermal calcite and quartz coexisting with the iron minerals contain principally fluid, which were homogenized into liquid phase. The homogenization temperature (TH (L-V) ) and the salinity of the analysed fluid inclusions range from 129°C to 270°C and from 0.4wt.% to 9.41wt.% NaCl eq., respectively. The δ 13 C PDB and δ 18 O SMOW values ranges from -2.15‰ to -5.77‰ (PeeDee Belemnite standard, PDB) and from +19.87‰ to +21.64‰ (Standard Mean Ocean Water standard, SMOW) in hydrothermal calcite veinlets occurring with iron minerals and -0.66‰ to -4.37‰ (PDB) and +15.55‰ to +20.14‰ (SMOW) within the host carbonates, respectively. The field relations and petrographic examination along with geochemical and isotopic considerations indicate that the Pivehzhan iron deposit was formed through replacement processes by reducing and acid fluids containing light carbon and oxygen isotopes. Variations in the physico-chemical conditions of hydrothermal fluids and their interaction with carbonates were the most effective mechanisms in the formation of this iron deposit. The potential source of iron was probably the basement magmatic rocks from which iron was leached by hydrothermal solutions.

Genesis of the Weibao banded skarn Pb-Zn deposit, Qimantagh, Xinjiang: Insights from skarn mineralogy and muscovite 40Ar-39Ar dating

The Weibao Pb-Zn deposit is located in the Qimantagh area, Xinjiang (NW China). At Weibao, stratiform Pb-Zn ore bodies are hosted by the skarn-altered Mesoproterozoic Langyashan Formation. Both of the skarn rocks and Pb-Zn ores are banded. The skarn bands are normally 0.5 to 5cm wide and comprise alternating garnet and pyroxene zones. Systematic mineralogical studies indicate that the Weibao banded skarn was formed by infiltrative metasomatism of magmatic fluids in a disequilibriated geochemical system, rather than by the bimetasomatism between marble and Si-Al units or the metamorphism of calc-silicate-rich submarine exhalative beds. This infiltrative metasomatic process can be further divided into four stages, namely the prograde skarn, retrograde skarn, sulfide and carbonate stage. Three garnet types (Garnet I, II and III) and two pyroxene types (Pyroxene I and II) have been identified at Weibao. Garnet I has commonly Fe-rich core and Al-rich rim (Ad34Gr65 to Ad96Gr3), while Garnet II has a wider composition range (Ad23Gr73 to Ad97Gr2; average: Ad59Gr41). Garnet III is compositionally more homogeneous and Mn-rich (Ad17Sp3Gr80 to Ad55Sp6Gr39; average: Ad47Sp4Gr49). Pyroxene I is diopside-rich (Hd20Jo1Di79 to Hd36Jo2Di62; average Hd29Jo1Di70), while Pyroxene II has lower diopside component (Hd34Jo3Di63 to Hd55Jo13Di32; average: Hd48Jo5Di47). Garnet I and Pyroxene I may have formed by a small volume of high-temperature and volatile-rich fluids exsolved from the magmas at its initial crystallization stage. Further fractionation generated abundant magmatic fluids that reacted with the impure carbonates through infiltrative metasomatism, forming Garnet II and Pyroxene II in the banded skarn. Garnet III occurs as garnet+sphalerite+galena+calcite veinlets crosscutting the early-stage pyroxene and garnet zones, and may have been a product of late hydrothermal superimposition.Sulfide stage is the main ore-forming stage at Weibao. Sulfide minerals in this stage precipitated mainly through replacing anhydrous (e.g., pyroxene) and hydrous (e.g., amphibole) minerals, or as interstitials among early-formed minerals. A minor amount of the sulfides also occurs as sulfide veins. The sulfide precipitation may have been controlled chiefly by physicochemical changes of ore-forming fluids and the characteristics of early-formed skarn minerals. Specifically, hydrothermal replacement of skarn minerals has provided the space for sulfide to precipitate and thus controlled their distribution, and further shaped the mineralization into a banded structure. 40Ar-39Ar dating of the syn-mineralization muscovite yielded a Late Triassic age (ca. 226Ma), which was coeval to the massive post-collisional intermediate-felsic granitoids emplacement in the Qimantagh area. Magmatic fluids evolved from these intermediate-felsic granitoids have induced the regional-scale magmatic hydrothermal mineralization, including that at Weibao.

Физико-химические условия формирования золотосодержащих магнетит-хлорит-карбонатных пород в Карабашском массиве гипербазитов (Южный Урал)

In the paper, there are adduced the data of a thermobarogeochemistry investigation of fluid inclusions in apatite of magnetite-chlorite-carbonates rocks from ultrabasite Karabash massife. The rocks are carrying copper-bearing aurum (1.3-2.6 wt % Cu) and was formed at temperature in the range of 480-280°C and a pressure of about 2-3 kbar. The content of the inclusions corresponds to the salt system of H 2 O-NaCl and the salt concentration in the solution 3.7-8.8 wt % eq. NaCl. Fluids gas components, extraction by pirolysis up to temperature 450°C, are described by a system C-H-O with an insignificantly amount of nitrogen. In fluid composition presents a small amount of the reduced gasses - CO, H 2 , CH 4 , hard carbon-hydrates (C 2 H 4 , C 2 H 6 , C 3 H 6 , C 3 H 8 etc.). Adduced comparative analysis of fluid composition and the degree of oxidation fluid gas component (O fl = CO 2 /(CO 2 + CO + H 2 + CH 4 ) during the forming magnetite-chlorite-carbonate rocks, the rodingites and the listwenites. It is established, that carbon acid part of mole in fluid (X CO2 ) grown from extremely low value by the forming of rodingites with copper-bearing aurum ( CO2 . In the same time, reduction regime of the forming rodingites (O fl = 0.14-0.35) is replaced on oxidation one by the forming of magnetite-chlorite-carbonate rocks (O fl = 0.73-0.92), calcite veinlets, in the rodingites (O fl = 0.83) and also the listwenites (O fl = 0.77).

Geochemistry and diagenetic history of the Ordovician Lower Head Formation sandstones, western Newfoundland, Canada

The Lower Head Formation in the Parson’s Pond area (western Newfoundland, Canada) comprises siltstones with very fine grained to fine-grained sandstones. Petrography confirms that these sandstones are matrix rich, essentially wackes, with detrital minerals including quartz, feldspar, biotite, and numerous accessory minerals. Observed petrographic features suggest that the Lower Head sediments are the distal product of erosion, with sediment sourced from the Dashwoods microcontinent and Lushs Bight oceanic tract and thoroughly mixed in an earlier basin prior to final deposition in a trench slope basin. The Lower Head Formation sandstones have low porosity, with early diagenetic cements (C1) and later calcite in crosscutting calcite veinlets (C2). Petrographic, isotopic, and fluid inclusion analyses indicate that C1 cements formed during the early stages of diagenesis. Both δ13C and δ18O isotopes for the C1 calcite cements are isotopically heavier than the C2 calcite veins. Fluid inclusion homogenization temperatures for the later crosscutting C2 calcite generally range between 78 and 116 °C, with a mean of 100.7 °C (±9.75 °C) and fluid salinities of 5.41–15.98 equiv. wt.% NaCl. Fluid inclusion gas analysis from C2 calcite confirms that CO2/CH4 generally has an inverse correlation with N2/Ar. Petroleum-bearing fluid inclusions were also recorded in C2 calcite cements, indicating that these fractures were conduits for hydrocarbon migration prior and (or) during cementation. However, the early cementation and associated low porosity of the Lower Head Formation sandstones indicate that they offer restricted pathways to migrating fluids and volatiles, and any hydrocarbon migration must have been fracture controlled.

Ferriakasakaite-(La) and ferriandrosite-(La): new epidote-supergroup minerals from Ise, Mie Prefecture, Japan

AbstractThe newREE-rich, monoclinic, epidote-supergroup minerals ferriakasakaite-(La) and ferriandrosite-(La), found in tephroite calcite veinlets cutting the stratiform ferromanganese deposit from the Shobu area, Ise City, Mie Prefecture, Japan, were studied using electron microprobe analysis and single-crystal X-ray diffraction methods. Ferriakasakaite-(La), ideallyA1CaA2LaM1Fe3+M2AlM3Mn2+(SiO4)(Si2O7)O(OH) (Z= 2, space groupP21/m), has a new combination of dominant cations atA1(Ca) andM3(Mn2+), which are the key sites to determine a root name for epidote-supergroup minerals. The unit-cell parameters area= 8.8733(2),b= 5.7415(1),c= 10.0805(3) Å, β = 113.845(2)° andV= 469.73(2) Å3. According to the structural refinement (R1= 3.13%), the determined structural formula isA1(Ca0.54Mn2+0.46)A2[(La0.48Ce0.20Pr0.07Nd0.18Gd0.02)Σ0.95Ca0.05]M1(Fe0.423+V0.343+Al0.18Ti0.064+)M2(Al0.96Fe0.043+)M3(Mn0.502+Fe0.432+Mg0.07)(SiO4)(Si2O7)O(OH). Ferriandrosite-(La), ideallyA1Mn2+A2LaM1Fe3+M2AlM3Mn2+(SiO4)(Si2O7)O(OH) (Z= 2, space groupP21/m), is theM1Fe3+analogue of androsite. The unit-cell parameters area= 8.8779(1),b= 5.73995(1),c= 10.0875(2) Å, β = 113.899(1)° andV= 469.97(2) Å3, and the structural formula isA1(Mn0.562+Ca0.44)A2[(La0.49Ce0.20Pr0.08Nd0.19Gd0.02)Σ0.97Ca0.03]M1(Fe0.403+V0.283+Al0.20Fe0.052+Ti0.074+)M2(Al0.97Fe0.033+)M3(Mn0.502+Fe0.402+Mg0.10)(SiO4)(Si2O7)O(OH) (R1= 2.93%). The two new minerals, which are compositionally very similar overall, are distinguished by occupancy ofA1, Cavs. Mn2+. The structural properties of these minerals depend not only on theREEcontent atA2, but also on the Mn content atA1.