Hydrogeochemistry of porphyry related solutes in ground and surface waters; an example from the Casino Cu-Au-Mo deposit, Yukon, Canada

The Casino Cu-Au-Mo deposit is one of the largest and highest-grade porphyries of its kind in Canada, residing in an unglaciated region of west central Yukon. A batch of 22 stream water samples and eight groundwater samples were collected proximal to the deposit for the purpose of identifying the most diagnostic trace element and isotopic pathfinders associated with the hydrothermal mineralization, as well as establishing natural hydrogeochemical baselines for the area. Water chemistry around this deposit was investigated because: (i) the deposit has not yet been disturbed by mining; (ii) the deposit was known to have metal-rich waters in local streams; and (iii) the deposit has atypically preserved ore zones. Surface and ground waters around the Casino deposit are anomalous with respect to Cd (up to 5.4 µg/L), Co (up to 64 µg/L), Cu (up to 1657 µg/L), Mo (up to 25 µg/L), As (up to 17 µg/L), Re (up to 0.7 µg/L), and Zn (up to 354 µg/L) concentrations. Sulfur and Sr isotopes are consistent with proximal waters interacting with the Casino rocks and mineralization; a sulfide-rich bedrock sample from the deposit has δ34S = -1.2 ‰ and proximal groundwaters are only slightly heavier (-0.3 to 3.1 ‰). These geochemical and isotopic results indicate interaction and dispersion of porphyry related solutes in ground and surface waters and point to suitability of hydrogeochemistry as a medium for mineral exploration for porphyry-style mineralization in the Yukon, and elsewhere in Canada.Supplementary material: The physicochemical, major, trace, and isotopic data of stream and groundwaters used in this manuscript is publicly available as an Open File Report (OF 8823) from the Geological Survey of Canada.Thematic collection: This article is part of the Hydrochemistry related to exploration and environmental issues collection available at: https://www.lyellcollection.org/cc/hydrochemistry-related-to-exploration-and-environmental-issues

Ore Mineralogy, Geochemistry, and Dating (Re-Os, Ar-Ar) of the El Volcán Porphyry/Epithermal System, Maricunga Gold Belt, Northern Chile

The El Volcán gold project (8.9 Moz Au @ 0.71 g/t Au) is located in the Maricunga gold belt in northern Chile, on the flank of the large Cenozoic Copiapó Volcanic Complex. Precious metal mineralization is hosted in two zones (Dorado and Ojo de Agua) of (pervasively) altered Miocene porphyry intrusions and lava flows of andesitic to rhyolitic composition, and in breccias. The ore zones reflect an evolving magmatic-hydrothermal system with mineral assemblages of magnetite-ilmenite-pyrite-molybdenite (early), bornite-chalcopyrite-pyrite-rutile (stage I), chalcocite-chalcopyrite-enargite-fahlore-pyrite (stage II), and chalcopyrite-covellite-pyrite (stage III). Alteration is dominantly of Maricunga-style (illite-smectite-chlorite ± kaolinite), partly obscured by quartz-kaolinite-alunite ± illite ± smectite alteration. Powdery quartz-alunite-kaolinite alteration with native sulfur and cinnabar forms shallow steam-heated zones. Early K-feldspar ± biotite alteration is preserved only in small porphyry cores and in deep drill holes. Most gold is submicrometer size and is in banded quartz veinlets, which are characteristic of the Maricunga gold belt. However, some gold is disseminated in zones of pervasive quartz-kaolinite-alunite alteration, with and without banded quartz veinlets. Minor visible gold is related to disseminated chalcocite-chalcopyrite-enargite-fahlore-pyrite. The lithogeochemical database identifies a pronounced Au-Te-Re signature (>100× bulk crust) of the hydrothermal system. Molybdenum-rich bulk rock (100–400 ppm Mo) has an Re-Os age of 10.94 ± 0.17 Ma (2σ). 40Ar-39Ar ages on deep K-feldspar alteration and on alunite altered rock have the same age within error and yield a combined age of 11.20 ± 0.25 Ma (2σ). The formation of the El Volcán gold deposit took place during the establishment of the Chilean flat-slab setting in a time of increasing crustal thickness when hydrous magmas were formed in a mature arc setting. The vigorous nature of the hydrothermal system is expressed by abundant one-phase vapor fluid inclusions recording magmatic vapor streaming through a large rock column with a vertical extent of ≥1,500 m.

Comprehensive analysis and assessment of prospective gold-ore zones using modern geophysical methods

В статье рассматривается комплексный анализ геологической и геофизической информации по проводимым исследованиям с целью выделения перспективных участков для проведения дальнейших геологоразведочных работ. Цель работы. Провести комплексный анализ и оценку перспективных золоторудных зон с применением современных геофизических методов. Методы работы. Вертикальное электрическое зондирование методом вызванной поляризации, метод вызванной поляризации в модификации срединного градиента, геоэлектрические разрезы по профилям, аномалии поляризуемости поля электрических сопротивлений, метод ТЗ электротомографии. Результаты работы. Авторами в 2019 г. в северной части участка на площади 2,87 кв. км были выполнены работы СГ-ВП по сети 50×10м с MN – 10 м. и АВ – 2000 м. Измерения DU и φвппроводились на частоте 1.22 Гц измерителями МЭРИ – 24 и ЭИН – 209 (режим измерения частотный). Использовался генератор ГЭР – 5000 – 25 (мощность 5 кВт). По результатам измерений построены карты изолиний поляризуемости и кажущегося сопротивления. Следует отметить, что при определении сдвига фаз φвп в частотном режиме сигнал, используемый для измерения сдвига фаз при равных DU с импульсным режимом измерений в 30-100 раз выше. Это основное преимущество фазовых измерений над импульсными. Как видно из приведенного сравнения уменьшение длины приемной линии и шага наблюдений позволило увеличить детальность исследований СГ-ВП и выйти на уровень рудных тел, заданных в техническом задании. По результатам ТЗ электротомографии и ВЭЗ-ВП получены близкие результаты, хотя методически и теоретически ТЗ обладает в данных условиях большей детальностью и информативностью. По результатам геофизических работ построены карты изолиний и графиков ρк и φвп, выявлена их связь с рудовмещающими структурами и отдельными рудными телами. Всего выявлено 14 локальных аномалий поляризуемости связанных с золото-кварц-сульфидными и сульфидными рудными телами. Выявлены площадные аномалии повышенной поляризуемости и низких значений электрического сопротивления СГ-ВП вдоль Западной рудно-тектонической зоны. Они связаны с метасоматическими процессами в пределах Западной зоны сбросо-сдвигов. На площади работ отмечены слабоконтрастные аномалии магнитного поля в северо-западной части Северной зоны. Отмечено сильное влияние рельефа на характер магнитного поля, вследствие чего наблюдается корреляция хребтов с минимумами магнитного поля. The article discusses a comprehensive analysis of geological and geophysical information on ongoing research in order to identify promising areas for further exploration. Aim. Conduct a comprehensive analysis and assessment of promising gold ore zones using modern geophysical methods. Methods. Vertical electrical sounding by the induced polarization method, the induced polarization method in the modification of the median gradient, geoelectric sections along the profiles, anomalies of the polarizability of the electrical resistance field, TK method of electrotomography. Results. The authors in 2019 in the northern part of the site on an area of 2.87 sq. km SG-VP works were performed on a network of 50 × 10m with MN -10m. and AB - 2000 m. Measurements of DU and φvp were carried out at a frequency of 1.22 Hz with meters MARI - 24 and EIN - 209 (frequency measurement mode). Used generator GER - 5000 - 25 (power 5 kW). Based on the measurement results, maps of isolines of polarizability and apparent resistivity were constructed. It should be noted that when determining the phase shift φvp in the frequency mode, the signal used to measure the phase shift at equal DU with the pulse measurement mode is 30-100 times higher. This is the main advantage of phase measurements over pulsed ones. As can be seen from the above comparison, a decrease in the length of the receiving line and the step of observations made it possible to increase the detail of SG-VP studies and to reach the level of ore bodies specified in the terms of reference. Based on the results of the technical specification for electrotomography and VES-IP, similar results were obtained, although methodologically and theoretically, the technical specification has greater detail and information content under these conditions. Based on the results of geophysical work, maps of isolines and graphs of ρк and φвп were constructed, their relationship with ore-bearing structures and individual ore bodies was revealed. In total, 14 local anomalies of polarizability associated with gold-quartz-sulfide and sulfide ore bodies have been identified. Areal anomalies of increased polarizability and low values of electrical resistance of SG-VP were revealed along the Western ore-tectonic zone. They are associated with metasomatic processes within the Western fault-strike zone. Low-contrast magnetic field anomalies in the northwestern part of the Northern Zone were noted in the survey area. A strong influence of the relief on the nature of the magnetic field was noted, as a result of which a correlation of the ridges with the minima of the magnetic field is observed

Colusite from the Plavitsa gold deposit – a new mineral for the Republic of North Macedonia Gotse Zlatkov

The Plavitsa ore deposit is a part of the Zletovo ore field. Two ore zones were established: primary (sulphide) and secondary (oxide, gold-bearing). The colusite occurs at the primary sulphide ore zone. The results of the microprobe analyses in wt%: Cu 47.38, V 3.41, Sn 8.28, As 10.75, Sb 2.01, Fe 0.11, S 29.1. LA-ICP-MS revealed contents of Te, Se, In, Ag, and Au. The micro-hardness (H) is 280–310 kg/mm2. At λ 540 and 580 nm R is 29% and 29.6%. The colusitе associates with enargite, famatinite, luzonite, bornite, barite, tennantite, tetrahedrite and tellurides of Au and Ag.

The Westwood Deposit, Southern Abitibi Greenstone Belt, Canada: An Archean Au-Rich Polymetallic Magmatic-Hydrothermal System—Part II. Hydrothermal Alteration, Mineralization, and Geologic Model

The Westwood deposit, located in the Archean Doyon-Bousquet-LaRonde mining camp in the southern Archean Abitibi greenstone belt, contains 4.5 Moz (140 metric t) of gold. The deposit is hosted in the 2699–2695 Ma submarine, tholeiitic to calc-alkaline volcanic, volcaniclastic, and intrusive rocks of the Bousquet Formation. The deposit is located near the synvolcanic (ca. 2699–2696 Ma) Mooshla Intrusive Complex that hosts the Doyon epizonal intrusion-related Au ± Cu deposit, whereas several Au-rich volcanogenic massive sulfide (VMS) deposits are present east of the Westwood deposit. The Westwood deposit consists of stratigraphically stacked, contrasting, and overprinting mineralization styles that share analogies with both the intrusion-related and VMS deposits of the camp. The ore zones form three distinct, slightly discordant to stratabound corridors that are, from north (base) to south (top), the Zone 2 Extension, the North Corridor, and the Westwood Corridor. Syn- to late-main regional deformation and upper greenschist to lower amphibolite facies regional metamorphism affect the ore zones, alteration assemblages, and host rocks. The Zone 2 Extension consists of Au ± Cu sulfide (pyrite-chalcopyrite)-quartz veins and zones of disseminated to semimassive sulfides. The ore zones are spatially associated with a series of calc-alkaline felsic sills and dikes that crosscut the mafic to intermediate, tholeiitic to transitional, lower Bousquet Formation volcanic rocks. The metamorphosed proximal alteration consists of muscovite-quartz-pyrite ± gypsum-andalusite-kyanite-pyrophyllite argillic to advanced argillic-style tabular envelope that is up to a few tens of meters thick. The North Corridor consists of auriferous semimassive to massive sulfide veins, zones of sulfide stringers, and disseminated sulfides that are hosted in intermediate volcaniclastic rocks at the base of the upper Bousquet Formation. The Westwood Corridor consists of semimassive to massive sulfide lenses, veins, zones of sulfide stringers, and disseminated sulfides that are located higher in the stratigraphic sequence, at or near the contact between calc-alkaline dacite domes and overlying calc-alkaline rhyodacite of the upper Bousquet Formation. A large, semiconformable distal alteration zone that encompasses the North Corridor is present in the footwall and vicinity of the Westwood Corridor. This metamorphosed alteration zone consists of an assemblage of biotite-Mn garnet-chlorite-carbonate ± muscovite-albite. A proximal muscovite-quartz-chlorite-pyrite argillic-style alteration assemblage is associated with both corridors. The Zone 2 Extension ore zones and associated alteration are considered synvolcanic based on crosscutting relationships and U-Pb geochronology and are interpreted as being the distal expression of an epizonal magmatic-hydrothermal system that is centered on the upper part of the synvolcanic Mooshla Intrusive Complex. The North and Westwood corridors consist of bimodal-felsic Au-rich VMS-type mineralization and alteration produced by the convective circulation of modified seawater that included a magmatic contribution from the coeval epizonal Zone 2 Extension magmatic-hydrothermal system. The Westwood Au deposit represents one of the very few documented examples of an Archean magmatic-hydrothermal system—or at least of such systems formed in a subaqueous environment. The study of the Westwood deposit resulted in a better understanding of the critical role of magmatic fluid input toward the formation of Archean epizonal intrusion-related Au ± Cu and seafloor/subseafloor Au-rich VMS-type mineralization.

The Westwood Deposit, Southern Abitibi Greenstone Belt, Canada: An Archean Au-Rich Polymetallic Magmatic-Hydrothermal System—Part I. Volcanic Architecture, Deformation, and Metamorphism

The Westwood deposit (4.5 Moz Au) is hosted in the 2699–2695 Ma Bousquet Formation volcanic and intrusive rocks, in the eastern part of the Blake River Group, southern Abitibi greenstone belt. The Bousquet Formation is divided in two geochemically distinct members: a mafic to intermediate, tholeiitic to transitional lower member and an intermediate to felsic, transitional to calc-alkaline upper member. The Bousquet Formation is cut by the synvolcanic (2699–2696 Ma) polyphase Mooshla Intrusive Complex, which is cogenetic with the Bousquet Formation. The deposit contains three strongly deformed (D2 flattening and stretching), steeply S-dipping mineralized corridors that are stacked from north to south: Zone 2 Extension, North Corridor, and Westwood Corridor. The North and Westwood corridors are composed of Au-rich polymetallic sulfide veins and stratabound to stratiform disseminated to massive sulfide ore zones that are spatially and genetically associated with the calcalkaline, intermediate to felsic volcanic rocks of the upper Bousquet Formation. The formation of the disseminated to semimassive ore zones is interpreted as strongly controlled by the replacement of porous volcaniclastic rocks at the contact with more impermeable massive cap rocks that helped confine the upflow of mineralizing fluids. The massive sulfide lenses are spatially associated with dacitic to rhyolitic domes and are interpreted as being formed, at least in part, on the paleoseafloor. The epizonal, sulfide-quartz vein-type ore zones of the Zone 2 Extension are associated with the injection of subvolcanic, calc-alkaline felsic sills and dikes within the lower Bousquet Formation. These subvolcanic intrusive rocks, previously interpreted as lava flows, are cogenetic and coeval with the intermediate to felsic lava flows and domes of the upper Bousquet Formation. The change from fractional crystallization to assimilation- and fractional crystallization-dominated processes and transitional to calc-alkaline magmatism is interpreted to be responsible for the development of the auriferous ore-forming system. The Westwood deposit is similar to some Phanerozoic Au ± base metal-rich magmatic-hydrothermal systems, both in terms of local volcano-plutonic architecture and inferred petrogenetic context. The complex volcanic evolution of the host sequence at Westwood, combined with its proximity to a polyphase synvolcanic intrusive complex, led to the development of one of the few known large Archean subaqueous Au-rich magmatic-hydrothermal systems.

Post-Ore Processes of Uranium Migration in the Sandstone-Hosted Type Deposits: 234U/238U, 238U/235U and U–Pb Systematics of Ores of the Namaru Deposit, Vitim District, Northern Transbaikalia

To assess the nature of the post-ore behaviour of uranium in the Namaru deposit (Khiagda ore field), U–Pb isotope systems and the isotopic composition of uranium (234U/238U and 238U/235U) were studied. The studied samples represent different ore zones of the deposit and were collected along cross-sections both vertically and horizontally. Wide variations in the isotopic composition of uranium and U–Pb isotopic age have been established. Deviations of the 234U/238U ratio from equilibrium values, which for some samples exceed 50%, along with significant variations in the isotopic age, indicate that permafrost layer, which covered the catchment areas of paleovalleys with meteoric oxygen-containing waters ca. 2.5 Ma ago, did not lead to preserving uranium ores at the deposit. Uranium migration took place during the Quaternary period. The effective combining the U–Pb dating and 234U/238U data in assessing the post-ore redistribution of uranium made it possible to recognize: removal of uranium from some zones of the ore body and its accompanying redeposition in others. Wide variations in the 238U/235U (137.484–137.851) ratios throughout the entire studied cross-sections can be explained by the different locations of samples relatively to the ore deposition front and change in redox conditions as this front advanced. Depletion of the light isotope 235U in the lower zone of the ore body may be associated with the influence of ascending carbonic waters established in the regional basement. The effect of such waters on uranium-bearing rocks causes predominant leaching of light 235U.

Geophysical Study of Gold Mineralized Zones in the Carolina Terrane of South Carolina

Large pyrite-dominated gold deposits are hosted in hydrothermally altered metamorphic rocks in the Carolina slate belt of South Carolina and are partly covered by Coastal Plain sedimentary rocks. In this study, we investigate the utility of geophysical data including aeromagnetic, electromagnetic (EM), and land gravity surveys as exploration tools. Observed geophysical anomalies are correlated with rock properties such as resistivity, susceptibility, and density. Mineral concentrations were measured for 40 samples from 16 new drill holes, as well as densities and pyrite concentrations for 49,183 samples from 448 drill holes in the Haile ore zone. Regional positive gravity anomalies are observed over the Haile, Ridgeway, and Barite Hill mine areas, and residual high-pass filtered positive gravity anomalies are observed over all mine areas. New measurements for drill cores in the Haile mine area directly confirm high rock densities and high pyrite concentrations in the ore zone. In the Haile and Brewer mine areas, high-conductivity EM anomalies are observed over the ore zones as well as over nearby metasedimentary rocks. The high concentration of pyrite in the metasedimentary units and in the ore zones may explain the high conductivities observed. All gold deposits in the Carolina slate belt are hosted in similar geologic settings near the contact between the Persimmon Fork metamorphosed volcaniclastic rocks and Richtex metamorphosed sedimentary rocks. Density and conductivity contrasts between the Persimmon Fork and Richtex Formation rocks may permit mapping of the contact zone between the two units. The magnetic anomalies do not correlate with the mineralized zones but rather with granite and gabbro plutons and diabase dikes. A prominent east-northeast linear magnetic anomaly correlates with the Modoc shear zone that separates low-grade metamorphic rocks of the Carolina terrane from higher-grade metamorphic rocks of the Kiokee belt. We use the Modoc linear magnetic anomaly to predict the southeastern boundary of the Carolina slate belt where it is covered by Coastal Plain sedimentary rocks.

Structure of the Golets Vysochaishy gold deposit (Northern Transbaikalia)

The article describes the fold-thrust structure of the Golets Vysochaishy deposit located at the Baikal-Patom Upland in the Marakan-Tunguska megasyncline. The latter is composed of terrigenous-carbonate carbonaceous rocks metamorphosed in greenschist facies conditions. The deposit is detected in the hanging wing of the asymmetric Kamenskaya anticline. In a cross section, the anticline is an S-shaped structure extending in the latitudinal direction. The main feature of the Golets Vysochaishy deposit is the development of interlayer sulfidization zones (pyrite, pyrrhotite), including gold-bearing ones. Its gold-ore zones tend to occur in layered areas of interlayer sliding in the rocks of the Khomolkhinskaya suite.Four structural markers revealed within the deposit area are indicative of repeated deformation processes: (1) sublatitudinal folding, cleavage of the axial surface and its subsequent transformation into schistosity; (2) crenulation cleavage; (3) interlayer sliding and rock breakdown with interlayer drag folds, parallel microfractures and polished slickensides; (4) large quartz veins and veinlets that cross cut the main structural elements in plan.