Gold Occurrences Research Articles

Gold Mineralization in the Kyaikhto District, Mon State, Southern Myanmar

The Kyaikhto gold district is located within the Slate Belt and Mogok Metamorphic Belt of Southern Myanmar. The study area is covered by Carboniferous to Lower Permian metasedimentary rocks consisting of slate, phyllite, and schist of the Mergui Group, intruded by later igneous rocks. Four gold occurrences have been identified in the Kyaikhto district: the Kunzeik in the north, Zibyaung, and Thae Phyu Chaung in the center and Meyon in the south. Gold mineralization in the Kyaikhto district is associated with sheeted, stockwork, dissemination, and sulfide-bearing quartz veins. Ore minerals recognized include sphalerite, galena, chalcopyrite, molybdenite and pyrite with minor native gold and electrum. Two types of fluid inclusions were examined in the quartz samples of the Kunzeik and Zibyaung—Type A: aqueous carbonic fluid inclusions and Type B: aqueous fluid inclusions. At the Kunzeik, Type A fluid inclusions homogenize at temperatures from 296°C to 376°C with low salinities (1.6 - 4.6 wt% NaCl equivalent). The homogenization temperatures of Type B fluid inclusions in vein quartz range from 246°C to 312°C, with salinities of between 1.2 and 10.7 wt% NaCl equivalent. In the Zibyaung, the homogenization temperatures of Type A inclusions vary from 305°C to 378°C, with salinities from 4.6 to 9.6 wt% NaCl equivalent. The homogenization temperatures of Type B fluid inclusions mainly range from 242°C to 298°C, with salinities from 0.9 to 11.8 wt% NaCl equivalent. These characteristics of fluid inclusions are similar to those of orogenic gold mineralization systems.

Geological Context Mapping of Batouri Gold District (East Cameroon) from Remote Sensing Imagering, GIS Processing and Field Works

The Batouri area is located in the Adamawa-Yade domain in East Cameroon region, and has a high geological potential as a host for gold deposits. It is covered by thick forest where outcrops are sometime scarce. The purpose of this study is to generate and combine different geological information which makes up the specificity of the Batouri gold District, in order to contribute to the better knowledge of its geological setting. From satellite imageries, GIS tools and field data; lithological units, lineament and density maps have been dressed at regional-scale of 1/400.000. The mapping has enabled the discovery of spatial and topologic relationships between shear zones, lineaments, gold occurrences and often mineralized granitic intrusions. According to the field data, lithological and lineament maps, the lithology of the Batouri gold District is characterized by alkali granitoids (tonalite, granodiorite, syenomonzo-granite, alkaline granite) hosted by orthogneisses and migmatites as gold mineralization hosts; while the lineaments show a major shear zones trending NE-SW defined by presence of mylonites. The shear zones crosscut all lithologies, mostly granodiorite where majority of gold occurrences is observed; locally, nearest these shear zones, rocks are transformed to the mylonites and gold is concentrated along. From density map, it is shown that the high gold mineralization zone corresponds to highest lineaments density. All those data suggest that gold mineralization in the Batouri district is controlled by tectonic and lithology. It is conclusive that Batouri gold deposit is epigenetic gold set emplaced in orogenic setting, during the post-collisional stage of the Central African Fold Belt (CAFB) and the Congo Craton (CC).

Aeromagnetic Investigation of Geologic Structures Associated with Gold Mineralization along Danja, Northwestern Nigeria

The study area falls within the basement complex of northwestern Nigeria and covers four adjacent quarter degree sheets of Funtua, Malumfashi, Masks and Zaria. Gold occurrence in the area was not reported until the recent discovery by artisanal miners. Previous works have shown that primary gold mineralization within the Nigerian basement complex is controlled by geologic structures where they act as conduits for fluids flow and as loci for mineralization. This paper is aimed at characterizing the major structural controls of gold mineralization in the study area. This was achieved by determining depth to basement, producing a magnetization map showing magnetic susceptibility range across the entire study area, and a model of the shape, location and depth of structures in the study area. The anomalies on the aeromagnetic map were defined by fitting a first order polynomial to the total fields, by the method of least squares to obtain the residual field data. First vertical derivative and analytic signal computed, defined distinct pattern of the magnetic signatures. Depths to the surface of the geologic structures (which appears as lineaments on aeromagnetic maps) were obtained from Euler deconvolution solutions which gives an average depths range of 200.2 m to 2229.1 m, with very few solutions having depths less than 300 m. The most prominent lineament and all major subtle lineaments have a depth range of 200 m to 600 m which shows that the structures are deep seated. The magnetic susceptibility values obtained from the magnetization map ranges from 0.000666 to 0.000996 SI. The lineament expected to be the major conduit for possible fluid flow that emplaced the Gold mineralization in the area is suspected to be the continuation of Kalangai fault which trends NE-SW along Malumfashi in the study area.

The role of airborne geophysics in the investigation of gold occurrences in the Itapetim Region, Borborema Province, Northeast Brazil

Abstract We present a combined analysis of airborne geophysical data (magnetics and gamma-ray spectrometry) and field aspects of Itapetim lode gold district region, aiming to identify structurally deformed and hydrothermally altered zones, which are suggestive of gold mineralized sectors. The main geophysical lineaments are oriented in the NE-SW and E-W directions and display a clear correlation with the major gold-bearing structures in the region. In the magnetic maps, the key pathfinder for gold occurrences is their association with strongly magnetized areas positioned along the Itapetim Shear Zone and outer contour of Teixeira Batholith. In the field, such structures are materialized in protomylonitic and mylonitic rocks that present evidence of ductile and brittle deformation, whereas kinematic criteria are suggestive of a transpressional tectonic regime. In addition, the main radiometric pattern is characterized by K enrichment, which is correlated with a hydrothermal mineral assemblage dominated by quartz, potassium feldspar, and tourmaline. Based on the obtained data integration, we produced an integrative map and located ten new target areas of possible gold mineralization, which is correlative to other well-known lode deposits in Northeast Brazil and Africa.

An integrated ore prospecting model for the Nyasirori gold deposit in Tanzania

ABSTRACT The Nyasirori gold deposit, located in the middle-western end of the Musoma-Mara Archean greenstone belt in Tanzania, is a tectonic altered rock type gold deposit controlled by shear tectonic zone. This work conducted high-precision ground magnetic measurements to delineate fault structures and favorable prospecting targets, utilized induced polarization (IP) intermediate gradient to roughly determine the distribution and extension of the tectonic altered zone and gold ore (mineralized) bodies, and further carried out IP sounding and magnetotelluric sounding to locate the tectonic altered zone and gold ore (mineralized) bodies. The anomalous gradient belt of the combination of positive and negative micromagnetic measurements reflects the detail of shallow surface tectonic alteration zone and gold mineralization body. Micromagnetic profile anomalies indicate the spatial location and occurrence of concealed tectonic alteration zone and gold (mineralized) ore bodies. Soil geochemical measurements indicate that the ore-forming element Au correlates well with As and Sb, and As and Sb anomalies have a good indication to gold orebodies. Based on the multi-source geological-geophysical-geochemical information of the Nyasirori gold deposit, this work established an integrated prospecting model and proposed a set of geophysical and geochemical methods for optimizing prospecting targets.

New orogenic type gold occurrences in the Uyanga ore knot (Central Mongolia)

The Uyanga ore knot district of the Khangay metallogenic zone are hosted by the lower-middle Devonian volcanogenic-sedimentary Erdenetsogt formation. About 40 samples were collected from the host rocks, veins and quartz veins in the Uyanga ore knot district in 2016. The new Burgetei, Ult and Senjit gold occurrences were studied. The quartz-sulfide, gold-arsenic and gold-antimony-mercury mineralization are determined in the berecitization, silicification, limonitization and glauconization altered metasomatic zones within the Uyanga ore knot districts. The rocks of the Erdenetsogt formation have an irregular gold content: 0.96 g/t Au is determined in quartz vein taken from trench of the Burgetei occurrence (BG-7/16), Au content is highest up to 3.5 g/t in the quartzite-jasper (Ult-7/16 and Ult-9/16) cut by quartz veins in the Ult occurrence. The Senjit occurrence represents Au-Hg-Sb epizonal level of orogenic gold deposits structure with highest Hg content up to 851 ppm. This year no sulfide minerals were found in the siltstone of this occurrence. The Au content of arsenical pyrite of the Burgetei and Ult is below the detection limit by electron microprobe analysis. The Au content of arsenopyrite of the Ult occurrence is highest (up to 238 ppm). Therefore, the ore-mineral assemblages in the gold occurrences reflect the differences between the three explored sites, formed in the course of fluid evolution during the fluid-rock interaction. Variable concentrations of indicative elements (As, Te, Sb, Hg) and their ratios confirm this fact. The geodynamic position, the type of the hydrothermal alteration of both igneous and sedimentary rocks, textures and mineral assemblages, the mineralization sequences are consistent with orogenic classification for the Burgetei, Ult and Senjit gold occurrences.

A geostatistical approach to analyzing gold distribution controlled by large-scale fault systems – An example from Côte d’Ivoire

Geostatistical approaches can help to understand the general characteristics of an area, to suggest feasible geological models, and to quantify overall patterns in the occurrence of economic mineralisation. We use such an approach to demonstrate the relationships between large-scale faults of various ages and kinematics, lithologies, and gold mineralisation to facilitate understanding of crustal-scale structural controls of gold deposits. Our example comes from Côte d’Ivoire, which is known to have undergone at least three major phases of deformation, two of which produced transpressional faults resulting from ESE-WNW and, later, NE/ENE-SW/WSW, compression. Using aeromagnetic and surface geological data, we interpret these faults and suggest a multiphase Riedel model for the region, taking fault reactivation into consideration. With the help of this simplified model, the spatial relationships between the faults, lithology, and 909 known gold occurrences, including 554 artisanal mining sites, are analysed within a GIS. Using geostatistical methods, gold mineralisation was found to probably be a two-stage process, with the later D2 stage potentially being the peak mineralization event. Gold occurrences are most abundant within c. 3 km of both newly formed and reactivated NE-SW faults, most importantly P1 and Y2 faults, in areas of low-intermediate fault density, and close to lithological contacts within the greenstone sequences.

3-D magnetic inversion and satellite imagery for the Um Salatit gold occurrence, Central Eastern Desert, Egypt

The Um Salatit is a gold occurrence situated in the Central Eastern Desert of Egypt. The studied area is characterized by an intensive imbrication zone of serpentinites and metavolcanic rocks. The integrated use of aeromagnetic and spectral reflectance remote sensing data has proved effective for mapping geology related to ore deposits. Spectral reflectance maps have been produced to discriminate various rocks, such as serpentinites, gabbros, and metavolcanic rocks. 3-D inversion of aeromagnetic data acquired over the Um Salatit study area produced a 3-D magnetic susceptibility model showing magnetic bodies surrounded by less magnetic host rock. The magnetic features are elongated ENE-WSW parallel to the major thrust fault and mapped the Um Salatit serpentinized rocks. Remote sensing data allow investigating surficial geological features and mapping the mineralized areas. Remote results, in conjunction with 3-D inversion of aeromagnetic data, demonstrate that gold occurrence in the study area was effectively restricted to the highly magnetic zone interpreted as host rocks.

The use of ASTER data and geochemical analyses for the exploration of gold at Samut area, South Eastern Desert of Egypt

The present study investigates the use of ASTER and geochemical data in the exploration of new gold occurrences in altered granodiorite rocks at Samut area in the South Eastern Desert of Egypt. The mapping approach developed and applied in this study integrates image ASTER and field data sets to produce a map showing the alteration zones within granitoid rocks in the Samut area. Due to the differences in hydrothermal mineral components as well as their intensities and influences on the surrounding rocks, various alteration processes have been occurred within the host granodioritic rocks. Such alteration processes include sericitization, chloritization, silicification, and ferrugination, resulted from the chemical interaction between the host rock minerals and mineral bearing ascending solutions. Each alteration process is characterized by significant minerals. The sericite and altered plagioclase characterize the sericitization process, whereas biotite, muscovite, chlorite, and hornblende minerals are associated with chloritization. However, silicification process is manifested by the quartz veins and fractured quartz grains. The ferrugination process is characterized by the transformation of magnetite to hematite and goethite. The chemical analyses of the unaltered granodiorites yielded Au content between 0.01 and 1.61 ppm, while in the altered granodiorite; Au content is around 0.02 to 14.79 ppm. The presence of gold in the unaltered and altered granodiorite even in a low percentage, but in huge tonnages gives an importance and makes the study area worthy of gold exploration and possible exploitation and hence international propagation. The Samut district is made up of intermediate to acidic metavolcanics intruded by a hornblende granodioritic pluton and cut by acidic dykes and quartz veins and veinlets. The associated hydrothermal activity with the plutonic intrusion led to the occurrence of promising alteration zones for gold in the granodiorite.

Textures and trace element signatures of pyrite and arsenopyrite from the Gutaishan Au–Sb deposit, South China

The Gutaishan deposit is a slate-hosted lode Au–Sb deposit in the Xiangzhong Sb–Au metallogenic province, South China. The deposit has a proven reserve of ca. 9 -t gold at an average grade of 13-g/t and contains 2500-t Sb. The deposit represents the product of a complex ore-forming process, comprising four different stages, of which the third stage is the main gold–stibnite bearing stage. Scanning electron microscopy, electron probe microanalysis, and laser ablation inductively coupled plasma-mass spectrometry were used to investigate the occurrence of visible gold and the distribution of invisible gold in pyrite and arsenopyrite. Visible gold displays textural complexity with four distinct categories defined and assumed to have formed directly precipitated from ore-forming fluid and remobilized from pyrite and arsenopyrite. Pyrite and arsenopyrite occur as ten and four texturally distinct subtypes; all host invisible gold, which is lattice-bound. Trace element mapping of selected pyrite and arsenopyrite grains reveals a marked compositional zoning with respect to Au and other elements in both minerals. Observed decoupled behavior between Au and As in some grains contradicts the paradigm of coupled Au and As substitution. Evidence suggests that the Gutaishan deposit likely represents an evolving Au–Sb mineralization event recorded by the complex texture and geochemical signatures of visible gold, sulfides, and sulfosalts.

COMPLEX GOLD-MOLYBDENUM DEPOSITS AND OCCURRENCES IN GREENSTONE BELTS OF THE MIDDLE DNIPRO REGION OF THE UKRAINIAN SHIELD

The most important molybdenum mineralization of the Middle Dnipro province is limited to the Mesoarchean (3,1–2,9 Ga) Greenstone belts or structure (GSS). These are next occurrences: East-Sergiivka, Solone in the Sura GSS and Gannivka (district “Chervona”) in the Kryvyi Rih GSS. They have spatial combining or closeness with well-known gold deposits and occurrences: East-Sergiivka and Solone occurrences are located on the Eastern flanks of the Sergiivka and Balka Zolota deposits, respectively, in the sublatitudinal ore-bearing zones. From the West to the East gold mineralization gradually changes to gold-molybdenum and molybdenum. Gannivka molybdenum and Zhovtіanka gold occurrences are adjacent and localized in the submeridional zone of the Kryvyi Rih-Kremenchuk fault, and not spatially combined. However, similar to the etalon Lobash deposit, they can be combined as elements of a common ore-generating system related to a submeridional-extended granite massif undiscovered by erosion. In the process of previously performed geological surveys and related research, these ore prospects were studied and evaluated separately for each type of minerals. It is proposed to carry out further geological research in the context of spatially and genetically combining of gold and molybdenum mineralization. First of all it concerns deposits and occurrences of Sura GSS, where it is rationally to place two complex gold-molybdenum deposits: Sergiivka and Balka Zolota. This approach, which involves carrying out mining and exploration works on a joint scientific and technical base for molybdenum and gold ores, will undoubtedly have good economic efficiency and, ultimately, substantially increase the investment attractiveness of one or another deposit, facilitate the early launch industrial exploitation.

Genesis of the Sulfide Hosted Refractory Gold Occurrences within the Carbonaceous Metasedimentary Units of the Dalma Volcano-sedimentary Basin, North Singbhum Mobile Belt, Eastern India

Paleo-Mesoproterozoic (1.0-2.4 Ga) north Singhbhum mobile belt (NSMB) is one of the prominent polymetallic mineral belt within the Singhbhum crustal province of eastern India lying between Chotanagpur gneissic complex (CGC) in the north and the Archaean Singhbhum craton (>2.4 Ga) in the south. The study area is located along the northern fringe of Dalma volcano-sedimentary basin. Lithological variations, structure, metamorphism and tectonic setting indicate good prospect for regional gold exploration within this area.Extensive work by Geological Survey of India (GSI) within this basin reveals gold occurrences with its concentrations ranging from 0.1 to 4 ppm within the carbonaceous cherty quartzite. Gold mineralization within the area has been reported to be associated with quartz ± quartz carbonate vein either as disseminated gold or as refractory gold within the sulfides. A detailed study on the occurrence of refractory gold associated with carbonaceous cherty quartzite has not been carried out by any of the previous workers. The present work report the occurrence of refractory gold associated with sulfides within the carbonaceous host rocks. Detailed petrographic studies of the carbonaceous host rock reveal the presence of sulfides such as pyrrhotite, pyrite, chalcopyrite, arsenopyrite. EPMA studies of the host rocks indicate the presence of invisible gold within the sulfides varying in concentration from 100 to 1000 ppm. Total organic carbon (TOC), high resolution X-ray diffraction (HR-XRD) and Fourier transform infrared spectrometry (FTIR) analysis show the presence of organic carbon within the samples. Presence of organic carbon facilitates reducing environment required for gold mineralization within carbonaceous host rock in the study area.

Delineation potential gold mineralization zones in a part of Central Eastern Desert, Egypt using Airborne Magnetic and Radiometric data

Localization of probable gold mineralization zones in a selected part of the central Eastern Desert of Egypt has been executed by mapping lithology, structures and hydrothermal alteration zones. In this regard, both aeromagnetic and aeroradiometric data have been utilized in the analysis; by making use of some enhancement techniques such as first vertical derivative, analytic signal and both Center for Exploration Targeting (CET) grid and porphyry. Also, ratio and ternary radiometric maps have been launched to aid in the interpretation process. The results indicated that the study area is dominant by NW, NNW, NNE, WNW, NE, E-W and N-S structural directions. The NW-SE was the most important one and considered as the preferred orientation of ore deposits. Favorable regions of ore deposits were mapped and correlated well with known gold occurrences in the study area beside predicting new zones of mineralization. Analysis of aeroradiometric maps facilitates the correlation and delineation of lithological units based on the concentration of radioelements and ratios. Also, A number of hydrothermal alteration zones were mapped within younger granite, Hammamat felsites and Metasediments. Finally, A composite map consists of geology, structures and hydrothermal altered zones was generated using ArcGIS. Eight known locations of gold mineralization were investigated on this map and also new sites were suggested to be favorable locations for mineralization emplacement.

Epigenetic gold occurrence in a Paleoproterozoic meta-evaporitic sequence in the Rompas-Rajapalot Au system, Peräpohja belt, northern Finland

Epigenetic gold occurrence in a Paleoproterozoic meta-evaporitic sequence in the Rompas-Rajapalot Au system, Peräpohja belt, northern Finland

Regional geochemical baseline concentration of potentially toxic trace metals in the mineralized Lom Basin, East Cameroon: a tool for contamination assessment

The distribution of trace metals in active stream sediments from the mineralized Lom Basin has been evaluated. Fifty-five bottom sediments were collected and the mineralogical composition of six pulverized samples determined by XRD. The fine fraction (< 150 µm) was subjected to total digestion (HClO4 + HF + HCl) and analyzed for trace metals using a combination of ICP-MS and AAS analytical methods. Results show that the mineralogy of stream sediments is dominated by quartz (39–86%), phyllosilicates (0–45%) and feldspars (0–27%). Mean concentrations of the analyzed metals are low (e.g. As = 99.40 µg/kg, Zn = 573.24 µg/kg, V = 963.14 µg/kg and Cr = 763.93 µg/kg). Iron and Mn have significant average concentrations of 28.325 and 442 mg/kg, respectively. Background and threshold values of the trace metals were computed statistically to determine geochemical anomalies of geologic or anthropogenic origin, particularly mining activity. Factor analysis, applied on normalized data, identified three associations: Ni–Cr–V–Co–As–Se–pH, Cu–Zn–Hg–Pb–Cd–Sc and Fe–Mn. The first association is controlled by source geology and the neutral pH, the second by sulphide mineralization and the last by chemical weathering of ferromagnesian minerals. Spatial analysis reveals similar distribution trends for Co–Cr–V–Ni and Cu–Zn–Pb–Sc reflecting the lithology and sulphide mineralization in the basin. Relatively high levels of As were concordant with reported gold occurrences in the area while Fe and Mn distribution are consistent with their source from the Fe-bearing metamorphic rocks. These findings provide baseline geochemical values for common and parallel geological domains in the eastern region of Cameroon. Although this study shows that the stream sediments are not polluted, the evaluation of metal composition in environmental samples from abandoned and active mine sites for comparison and environmental health risk assessment is highly recommended.

Audio-magnetotelluric investigation of sulfide mineralization in Proterozoic–Archean greenstone belts of Eastern Indian Craton

Greenstone belts are well known for gold occurrences at different regions of the world. The Dhanjori basin in the eastern Singhbhum region shows major characteristics of a rifted greenstone belt. Initially, we conducted 14 audio-magnetotelluric (AMT) measurements for a profile of $$\sim $$ 20 km in the frequency range of 1 kHz to 10 Hz over this rather complex geologic environment covering Dhanjori Volcanics (DhV) and Kolhan Group (KG). Subsequently, gravity and magnetic surveys were also conducted over this AMT profile. The purpose of the survey was to identify and map conductive features and to relate them to metallogeny of the area along with the mapping of the basement of Dhanjori basin. The strike analysis showed $$\hbox {N30}^{\circ }\hbox {W}$$ strike for DhV for all the frequencies and for sites over KG domain in the frequency range of 100–10 Hz, but for KG domain, the obtained strike in 1 kHz to 100 Hz is $$\hbox {N45}^{\circ }\hbox {E}$$ . As the combination of transverse electric (TE), transverse magnetic (TM) and tipper (Tzy) can recover the electrical signature in complex geological environment, we discuss the conductivity model obtained from TE+TM+Tzy only. The inversion was carried for the regional profile with 14 sites and for 7 sites over KG domain. Conductivity model shows two well resolved conductors, one each in KG and Quartz Pebble Conglomerate Dhanjori (QPCD) domains respectively showing common linked concordant features between these regional and KG profiles. The conductors are interpreted as sulfide mineralization linked with QPCD group of rocks which may host gold. These conductors are also horizontally disposed due to the intrusive younger Mayurbhanj Granite. These intrusives correlate well with the gravity modeling as well. The thickness of the Dhanjori basin at the central is about 3.0 km, similar to that from gravity modeling. The conductivity model also indicates the presence of shallow conductors, but could not be resolved due to lack of high frequency data. However, the results from the close-by drill site indicate the presence of shallow sulfide mineralization hosting gold. The deep level conductors delineated from AMT studies are associated with gravity high and low magnetic. ICP-AES results of Dhanjori samples show significant concentration of gold $$\sim $$ 5.0 g/t, which is of economic consideration. Thus, it can be inferred that the conductors have evidences of sulfide mineralization which host gold.

Data for: Distinguishing Generations of Quartz and a Distinct Gas Signature of Deep High-Grade Carlin-Type Gold Mineralization Using Quadrupole Mass Spectrometry

Abstract Carlin-type gold deposits in north-central Nevada occur in a region that was the locus of igneous and/or hydrothermal activity over time and the overprinting of silicification associated with metamorphism, base metal mineralization, barren jasperoid, and post-ore alteration hinders exploration efforts. Therefore, the potential to distinguish unrelated generations of quartz using the results of quadrupole mass spectrometer (QMS) gas analyses was evaluated for the Getchell trend, and compared to results from the Goldstrike property in the Carlin trend and a Carlin-type gold occurrence in the Huijiabao trend, China. The results of fluid inclusion petrography, QMS analyses, and interpretation of gas data using N 2 –Ar–He ternary diagrams and CO 2 /CH 4 vs. N 2 /Ar plots indicate that different generations of quartz in the Getchell trend were deposited by hydrothermal fluids having distinct characteristics. Metamorphic quartz containing one-phase CH 4 and halite-bearing liquid–water dominant vapor-poor inclusions has the highest gas content (37.6 mol%) and highest N 2 /Ar values (3250), which are suggestive of an evolved magmatic fluid. Pre-ore and quartz–base metal veins contain CO 2 -bearing inclusions. Base metal veins have N 2 /Ar values ≥675 and a positive correlation between H 2 S/Ar vs. N 2 /Ar that is suggestive of a magmatic fluid. Carlin-type quartz contains liquid-dominant vapor-poor inclusions and is characterized by total gas contents >10 mol% and N 2 /Ar values >300 that are suggestive of mixed crustal–meteoric–magmatic fluid sources. Post-ore quartz and barren jasperoid formed from mixtures of gas-poor meteoric water and crustal fluids. Samples of deep high-grade mineralization from the Goldstrike property have total gas contents up to 10.5 mol% and N 2 /Ar values >300. Fluid sources include crustal, meteoric, and magmatic. Gas data from the Goldstrike property, Turquoise Ridge deposit, and metamorphic quartz of the Getchell trend plot near the N 2 apex of N 2 –Ar–He diagrams, which is indicative of a magmatic fluid end member. Carlin-type mineralization in the Huijiabao trend is unique because fluids were CH 4 -rich and there is a correlation between CH 4 and hydrocarbons. Gas analyses commonly record 2 is the dominant gas specie. Together, the results show that fluid inclusion gases can be used to distinguish different generations of quartz in mining districts with complex origins.

Distinguishing generations of quartz and a distinct gas signature of deep high-grade Carlin-type gold mineralization using quadrupole mass spectrometry

Carlin-type gold deposits in north-central Nevada occur in a region that was the locus of igneous and/or hydrothermal activity over time and the overprinting of silicification associated with metamorphism, base metal mineralization, barren jasperoid, and post-ore alteration hinders exploration efforts. Therefore, the potential to distinguish unrelated generations of quartz using the results of quadrupole mass spectrometer (QMS) gas analyses was evaluated for the Getchell trend, and compared to results from the Goldstrike property in the Carlin trend and a Carlin-type gold occurrence in the Huijiabao trend, China.The results of fluid inclusion petrography, QMS analyses, and interpretation of gas data using N2–Ar–He ternary diagrams and CO2/CH4 vs. N2/Ar plots indicate that different generations of quartz in the Getchell trend were deposited by hydrothermal fluids having distinct characteristics. Metamorphic quartz containing one-phase CH4 and halite-bearing liquid–water dominant vapor-poor inclusions has the highest gas content (37.6 mol%) and highest N2/Ar values (3250), which are suggestive of an evolved magmatic fluid. Pre-ore and quartz–base metal veins contain CO2-bearing inclusions. Base metal veins have N2/Ar values ≥675 and a positive correlation between H2S/Ar vs. N2/Ar that is suggestive of a magmatic fluid. Carlin-type quartz contains liquid-dominant vapor-poor inclusions and is characterized by total gas contents >10 mol% and N2/Ar values >300 that are suggestive of mixed crustal–meteoric–magmatic fluid sources. Post-ore quartz and barren jasperoid formed from mixtures of gas-poor meteoric water and crustal fluids.Samples of deep high-grade mineralization from the Goldstrike property have total gas contents up to 10.5 mol% and N2/Ar values >300. Fluid sources include crustal, meteoric, and magmatic. Gas data from the Goldstrike property, Turquoise Ridge deposit, and metamorphic quartz of the Getchell trend plot near the N2 apex of N2–Ar–He diagrams, which is indicative of a magmatic fluid end member.Carlin-type mineralization in the Huijiabao trend is unique because fluids were CH4-rich and there is a correlation between CH4 and hydrocarbons. Gas analyses commonly record <1 mol% total gas for evolved (crustal) and organic fluids. Fluid inclusions in post-ore quartz and barren jasperoid are also gas poor, but CO2 is the dominant gas specie.Together, the results show that fluid inclusion gases can be used to distinguish different generations of quartz in mining districts with complex origins.

Supergene gold enrichment in the Castromil-Serra da Quinta gold deposit, NW Portugal

ABSTRACTSeveral gold deposits hosted mainly by Variscan granites and Precambrian to Palaeozoic metasediments occur in the northwestern part of Portugal. Most of these deposits were mined by the Romans (in the period I BC to II AD) as open pits and surface galleries. The Castromil-Serra da Quinta gold deposit is an important example of such a mined site; it occurs in the Dúrico-Beirã Au province located in the Central Iberian Zone (CIZ) in the western branch of European Variscan belt, mainly on the eastern flank of the Valongo anticline. Open pits and underground galleries at Castromil-Serra da Quinta exploited the gossan formed from the weathering of primary mineralization. The gossan is composed essentially of goethite, scorodite and clay minerals. A recent drilling campaign at Castromil-Serra da Quinta has provided samples of the primary mineralization below the oxidation level. Different modes of gold occurrence are defined based on metallographic studies of both the gossan and drill cores. Gold I occurs encapsulated in primary sulfide minerals, mainly arsenopyrite and pyrite; Gold II is also associated with the main primary sulfides, but occurs along grain boundaries and in microfractures of the sulfides or in associated quartz veins; and Gold III occurs as free gold particles in iron oxides within the gossan. In the gossan samples, it is difficult to distinguish whether the gold particles hosted in oxides correspond to Gold I, Gold II, or both, so these particles are described as Gold I–II and they are commonly surrounded by very much smaller particles of Gold III. Scanning electron microscope (SEM) and electron probe microanalysis (EPMA) data for the different gold particles reveal that Gold I is poorer in Ag (~15.5–39.76%) than Gold II (37.46–51.45%), whereas Gold III corresponds to native gold (&lt;16.11% Ag). Gold III is thought to reflect gold enrichment in the upper level of the deposit, resulting from weathering processes that affected the primary Au (Bi) mineralization.

Background values of gold, potentially toxic elements and emerging high-tech critical elements in surface water collected in a remote northern European environment

A geochemical surfacewater survey, focused on 2nd and 3rd order streams, was carried out in the Oppdal/Berkåk area in Norway. Stream water was collected at 168 sample sites, covering a 1500-km 2 survey area. Electrical conductivity, pH, alkalinity and temperature were recorded in the field. Electrical conductivity and pH were also determined once more in the laboratory. The cations Br, Cl, F, NO 2 , NO 3 , PO 4 and SO 4 were determined by ion-chromatography (IC) on unacidified, laboratory filtered samples. Inductively coupled plasma quadrupole mass spectrometry (ICP-QMS) was used to analyse field filtered and acidified samples for 63 elements. In addition, inductively coupled plasma atomic emission spectrometry (ICP-AES) was used to determine 27 elements. One aim of the survey was to test whether today's ICP-QMS analyses are sensitive enough to directly use surface water efficiently for gold prospecting. The two known gold occurrences in the area are marked by low level Au anomalies in stream water (0.006 µg/l). These values are just above the detection limit of 0.001 µg/l and it must be concluded that today's detection limits are still not low enough to use stream water for routine Au (and In) prospecting. The anions as determined by IC were most problematic in terms of number of samples below detection limit. Increased anthropogenic activities in the lowlands are marked by slightly enhanced NO 3 values in the streams. An As, Mo, Sb, V anomaly marks the main skiing area near Oppdal but is probably geogenic. In general surface water geochemistry of, for example, Ca, Ce, Cu, K, La, Rb, SO 4 and Sr reflects the geology of the area well. Methodological tests indicate that it should be sufficient to take unfiltered samples in the field and to filter and acidify these in the evening at home base. The dataset provides a good overview of background concentrations and variation of almost 70 chemical elements in stream water from a remote northern European survey area. Supplementary material: Table S1 showing the analytical program, isotopes measured and detection limits, Table S2 with analytical results of the international reference materials used for quality control and Fig. S1 with geochemical maps for all elements are available at: https://doi.org/10.6084/m9.figshare.c.4012885