scholarly journals The Ag- and Au-bearing phases in the Escondida epithermal vein, Cerro Moro deposit, Santa Cruz, Argentina

2020 ◽  
Vol 58 (2) ◽  
pp. 191-201 ◽  
Author(s):  
Ana C. Mugas Lobos ◽  
María Florencia Márquez-Zavalía ◽  
Laura B. Hernández
Keyword(s):  
Partial Substitution ◽  
Critical Element ◽  
Santa Cruz ◽  
Epithermal Deposits ◽  
Fine Grained ◽  
Quartz Veins ◽  
Epithermal Mineralization ◽  
Ore Minerals ◽  
The Usa ◽  
Low Sulfidation

ABSTRACT The Cerro Moro deposit is located at 48°5′55″S, 66°39′1.6″W and 100 m.o.s.l. in Santa Cruz province, southern Argentina. It is a low sulfidation Au-Ag epithermal mineralization hosted by numerous NW–SE structurally controlled quartz veins developed in close spatial and temporal proximity to the products of Jurassic extension and magmatism. The Escondida vein is the most significant mineralized structure, as it hosts the base metal-rich and Au-Ag high grade mineralization. In this vein and the Zoe ore-shoot, ore minerals are abundant (sphalerite, galena, chalcopyrite, acanthite, and less abundant pyrite and marcasite) and frequently related to dark grey, fine-grained quartz with massive, porous, crustiform, and banded textures; variable quantities of fine-grained flakes of muscovite are locally present. The Ag- and Au-bearing mineral association is represented by acanthite, argyrodite, polybasite, pearceite, stromeyerite, mckinstryite, and jalpaite. Abundant acanthite occurs commonly associated with gold and silver; copper enrichments were detected and interpreted as nanoinclusions of Cu-bearing minerals. The occurrence of Se- and Te-enriched minerals (acanthite, argyrodite, polybasite, pearceite, stromeyerite, and mckinstryite), rather than silver selenides and/or tellurides, indicates the presence of reduced mineralizing fluids and may be ascribed to partial substitution of S by Se or Te. Polybasite and pearceite were differentiated by their chemistry. Although the presence of argyrodite in epithermal deposits with silver sulfosalts is relatively common, this first mention in Cerro Moro is highly encouraging for exploration for germanium, a critical element, which is also considered strategic by countries such as the USA and China.

Textural Characteristics of Barren and Mineralized Colloform Quartz Bands at the Low-Sulfidation Epithermal Deposits of the Omu Camp in Hokkaido, Japan: Implications for Processes Resulting in Bonanza-Grade Precious Metal Enrichment

2020 ◽  
Author(s):  
Lauren R. Zeeck ◽  
Thomas Monecke ◽  
T. James Reynolds ◽  
Erik R. Tharalson ◽  
Katharina Pfaff ◽  
...  
Keyword(s):  
Precious Metal ◽  
Precious Metals ◽  
High Grade ◽  
Metal Enrichment ◽  
Near Surface ◽  
Epithermal Deposits ◽  
Fine Grained ◽  
Precursor Phase ◽  
Ore Minerals ◽  
Low Sulfidation

Abstract The Miocene low-sulfidation epithermal deposits of the Omu camp in northeastern Hokkaido, Japan, are small past-producers of precious metals and represent significant exploration targets for high-grade Au and Ag ores. The quartz textures of ore samples and the distribution of ore minerals within quartz veins were studied to identify the processes that resulted in the bonanza-grade precious metal enrichment in these deposits. In the high-grade vein samples, which are crustiform or brecciated in hand specimen, ore minerals exclusively occur within colloform quartz bands. High-magnification microscopy reveals that ore-bearing colloform bands consist of fine-grained quartz exhibiting relic microsphere textures and quartz having a mosaic texture that formed through recrystallization of the microspheres. The presence of relic microspheres is evidence that the microcrystalline quartz hosting the ore minerals formed through recrystallization of a noncrystalline silica precursor phase. The ore-hosting colloform bands composed of agglomerated microspheres alternate with barren colloform quartz bands that are composed of fibrous chalcedonic quartz and mosaic quartz formed through recrystallization of the chalcedony. The findings of this study are consistent with previous models linking bonanza-grade precious metal enrichment and the formation of bands of noncrystalline silica in low-sulfidation epithermal veins to episodic vigorous boiling or flashing of the hydrothermal system in the near-surface environment.

scholarly journals The Distribution of Precious Metals in High-Grade Banded Quartz Veins from Low-Sulfidation Epithermal Deposits: Constraints from µXRF Mapping

Minerals ◽  
2019 ◽  
Vol 9 (12) ◽  
pp. 740 ◽  
Author(s):  
Erik Tharalson ◽  
Thomas Monecke ◽  
T. Reynolds ◽  
Lauren Zeeck ◽  
Katharina Pfaff ◽  
...  
Keyword(s):  
Precious Metals ◽  
Thermal Waters ◽  
High Grade ◽  
Epithermal Deposits ◽  
Quartz Veins ◽  
Ore Minerals ◽  
Low Sulfidation ◽  
Hand Specimen ◽  
Black Color ◽  
Representative Samples

High-grade ore zones in low-sulfidation epithermal deposits are commonly associated with the occurrence of banded quartz veins. The ore minerals in these veins are heterogeneously distributed and are mostly confined to ginguro bands, which can be identified in hand specimen based on their distinct dark gray to black color. Micro-X-ray fluorescence element maps obtained on representative samples of banded quartz veins show that Au occurs together with Ag minerals in some of the ginguro bands, but Au can also be present in quartz bands that are light gray to white and cannot be macroscopically distinguished from barren bands. The occurrence of compositionally distinct ginguro and gankin bands, the latter being a new term coined here for colloform quartz bands containing primarily electrum or native gold, can be explained by temporal changes in the composition of the ore-forming thermal waters or variations in the conditions of ore deposition. Textural relationships, including the dendritic shape of ore minerals that appear to have grown in a matrix of silica microspheres, suggest that the ginguro and gankin bands have formed as a result of rapid deposition associated with vigorous boiling or flashing of the thermal waters.

scholarly journals Textural Characteristics of Noncrystalline Silica in Sinters and Quartz Veins: Implications for the Formation of Bonanza Veins in Low-Sulfidation Epithermal Deposits

Minerals ◽  
2018 ◽  
Vol 8 (8) ◽  
pp. 331 ◽  
Author(s):  
Tadsuda Taksavasu ◽  
Thomas Monecke ◽  
T. Reynolds
Keyword(s):  
Power Plant ◽  
Precious Metal ◽  
Precious Metals ◽  
Fused Silica ◽  
Silica Microspheres ◽  
Textural Characteristics ◽  
Epithermal Deposits ◽  
Ore Minerals ◽  
Low Sulfidation ◽  
Ore Deposition

Silica sinters forming at the Wairakei geothermal power plant in New Zealand are composed of noncrystalline opal-A that deposited rapidly from cooling geothermal liquids flashed to atmosphere. The sinter is laminated with alternating layers of variably compacted silicified filamentous microbes encased by chains of fused silica microspheres. Microscopic inspection of bonanza quartz vein samples from the Buckskin National low-sulfidation epithermal precious metal deposit in Nevada showed that colloform bands in these veins exhibit relic microsphere textures similar to those observed in the silica sinters from the Wairakei power plant. The textural similarity suggests that the colloform bands were originally composed of noncrystalline opal-A that subsequently recrystallized to quartz. The colloform bands contain dendrites of electrum and naumannite that must have grown in a yielding matrix of silica microspheres deposited at the same time as the ore minerals, implying that the noncrystalline silica exhibited a gel-like behavior. Quartz bands having other textural characteristics in the crustiform veins lack ore minerals. This suggests that ore deposition and the formation of the colloform bands originally composed of compacted microspheres of noncrystalline silica are genetically linked and that ore deposition within the bonanza veins was only episodic. Supersaturation of silica and precious metals leading to the formation of the colloform bands may have occurred in response to transient flashing of the hydrothermal liquids. Flashing of geothermal liquids may thus represent a key mechanism in the formation of bonanza precious metal grades in low-sulfidation epithermal deposits.

scholarly journals Geology, Geochemistry and Hydrothermal Fluid Characteristics of Low Sulfidation Epithermal Deposit in the Sangon Area, Kokap, Special Region of Yogyakarta

2017 ◽  
Vol 2 (1) ◽  
pp. 48
Author(s):  
Pranayoga Pramumijoyo ◽  
Arifudin Idrus ◽  
I Wayan Warmada ◽  
Kotaro Yonezu
Keyword(s):  
Normal Fault ◽  
Wall Rock ◽  
Geological Condition ◽  
Alteration Zones ◽  
Quartz Veins ◽  
Ore Minerals ◽  
Ore Mineralization ◽  
Wall Rock Alteration ◽  
Low Sulfidation ◽  
Special Region

On the basis of the previous studies and reconnaissance survey in the studyarea covering Sangon, Kalirejo, Kokap Sub-district, Kulon Progo Regency, Special Region of Yogyakarta, it reveals some facts of the occurrence of quartz veins with massive, crustiform, comb, drusy cavity, saccharoidal, granular, and reniform/mammillated textures, the appearance of lattice bladed barite and hydrothermal breccia veins. Referring to those characteristics, the deposit type in the study area is interpreted to be low sulfidation epithermal type. This study is aimed to understand and characterize the geological condition, rock and ore geochemistry and the mineralizing fluids. The alteration and ore mineralization are almost observed in entire rock units particularly the intrusive andesite 1. Their formation is controlled by the tension fractures (NW–SE and NE–SW) which associate with sinistral strike slip faults (NE–SW), dilational jog (NNW–SSE), oblique normal fault (WNW–ESE), and predictable normal fault at the NE of study area (NW–SE). The alteration zones are developed to be silica-clay (quartz-illite-kaolinite-kaolinite/smectite), argillic (smectite-illite/smectite), and propylitic (chlorite-calcite±epidote). The precipitationof ore minerals is controlled by boiling, mixing, and wall-rock alteration, and canbe found in the quartz veins (quartz-adularia-sericite) and disseminated in the alteration zones, which their high variability is only can be found in the quartz veins, including pyrite, sphalerite, chalcopyrite, galena, marcasite, and arsenopyrite. Based on the ICPAES measurement of 5 quartz vein samples, the Cu, Zn, Pb, and As grade reach about 5,171 ppm, 8,995 ppm, 6,398 ppm, 34.1 ppm, and 1,010.5 ppm, respectively. Gold is not detected. Fluid inclusion microthermometric analysis shows Th of 242.1–257.6 °C and salinity of 1.57–3.87 wt.% NaCl equiv., which indicate a depth below the paleosurface of 384–516 m, and pressure of 101.7–136.6 bar. The ore deposit in the study area is interpreted to be a deep basemetal low sulfidation epithermal type. Gold might be depleted in this epithermal type.

scholarly journals Petrography, microthermometry, and isotopy of the gold veins from Vetas, Santander (Colombia)

2020 ◽  
Vol 24 (1) ◽  
pp. 5-18
Author(s):  
Sonia Rojas Barbosa ◽  
Juan Carlos Molano ◽  
Thomas Cramer
Keyword(s):  
Fluid Inclusions ◽  
Gold Mineralization ◽  
Coarse Grained ◽  
Fine Grained ◽  
Quartz Veins ◽  
Low Salinity ◽  
Second Stage ◽  
The Third ◽  
Jurassic Rocks ◽  
Low Sulfidation

The gold mineralization located in Vetas, Santander, consists of auriferous quartz veins hosted in Bucaramanga gneiss rocks, intrusive Jurassic rocks, and intrusive to porphyritic Miocene rocks. This study identified four mineralizing events: (1). Sericite, carbonate (ankerite and calcite?), massive and microcrystalline quartz, sphalerite, adularia, albite, galena, thin pyrite, pyrrhotite, chalcopyrite. The age for this stage is 10.78 ±0.23Ma (Ar/Ar on sericite). (2). Molybdenite, magnetite with exsolution of ilmenite, As-pyrite, sphalerite, fine-grained pyrite and little chalcopyrite quartz with huge, feathery, fine mosaic, flamboyant and microcrystalline textures and, tourmaline and sericite. (3). Gold and tennantite associated with sphalerite, fine- and coarse-grained pyrite, As-pyrite, chalcopyrite like inclusions, and quartz with flamboyant, mosaic, massive and “comb” textures, and tourmaline. Stage 2 and 3 happened from 7.58 ±0.15 Ma to 6,89±0,41Ma (Ar/Ar on sericite). (4). Thick, thin, and pyrite with arsenic, hematite and microcrystalline quartz (forming breccia texture), and sericite. The age for this stage is 5.24 ±0.10 (Ar/Ar on sericite). Post-mineral: quartz comb, alunite, halloysite, kaolinite, and ferrum hydroxides. The stable isotopes, ∂18O, ∂D, and ∂34S and fluid inclusions analysis infer that fluids were producing a mixture of meteoric and magmatic fluids with low salinity and minimum trapping temperatures between 200°C to 390°C. The mineralogy association, and fluid inclusions, in the first event show characteristic of low sulfidation epithermal. The second stage was hottest and with more magmatic signature over printed an intermediate sulfidation system; show a little more salinity on the fluids and more mineralogical diversity, the third and four events, could show an evolution of this fluid, where it was cooling and impoverishing on metals. Two initials stages are contemporaneous with two magmatic Miocene pulses on the area: the first one of granodiorite composition 10, 9± 0.2 Ma (U/Pb zircon), and the other one rhyodacite with 8.4 ±0.2 y 9.0 ± 0.2 Ma.

scholarly journals Gold Mineralization at the Maletoyvayam Deposit (Koryak Highland, Russia) and Physicochemical Conditions of Its Formation

Minerals ◽  
2020 ◽  
Vol 10 (12) ◽  
pp. 1093
Author(s):  
Evgeny G. Sidorov ◽  
Andrey A. Borovikov ◽  
Nadezhda D. Tolstykh ◽  
Daria S. Bukhanova ◽  
Galina A. Palyanova ◽  
...  
Keyword(s):  
Fluid Inclusions ◽  
Gold Mineralization ◽  
Fluid Pressure ◽  
Volcanic Belt ◽  
Physicochemical Characteristics ◽  
Epithermal Deposits ◽  
Quartz Veins ◽  
Mineral Associations ◽  
Epithermal Gold Deposit ◽  
Ore Minerals

Microthermometry study of fluid inclusions in quartz veins of the Maletoyvayam deposit (Koryak Highland, Russia) was carried out. This epithermal gold deposit contains unique Au compounds including maletoyvayamite, which has not been reported anywhere else. Two paragenetic mineral associations (pyrite-quartz and maletoyvayamite-quartz) with quartz of different generations corresponding to different pulses were also described. Only early generations of quartz (Q1) include ore minerals: pyrite for the first mineral assemblage, and in Au-bearing minerals, sulfosalts, bismuthinite, and others—for the second assemblage. A study on fluid inclusions in quartz showed a salinity (mainly NaCl + KCl) range from 0.2 to 4.3 wt.% NaCl eq., increasing from the first mineral association to the second due to boiling fluids. The obtained temperature variations for quartz crystallization were 295–135 °C, the fluid pressure ranged from 79 to 4 bar. On the other hand, the range of conditions obtained for the gold productive ore association is more narrow: salinity of the fluid inclusions is 4.3 wt.% NaCl eq., the temperatures vary from 255 °C to 245 °C, and the pressure from 39 to 32 bar. These physicochemical characteristics of the Maletoyvayam ore deposit greatly coincide with other HS-type epithermal deposits; however, within the Central Kamchatka Volcanic Belt it is so far the only deposit of this type reported.

scholarly journals Origin of the Kyaukmyet Low-Sulfidation Epithermal Gold Prospect, Monywa District, Central Myanmar

2021 ◽  
Vol 54 (1E) ◽  
pp. 1-18
Author(s):  
Toe Oo ◽  
Agung Harijoko ◽  
Lucas Setijadji
Keyword(s):  
Magmatic Fluid ◽  
Epithermal Gold ◽  
Quartz Veins ◽  
Mineral Assemblages ◽  
Epithermal Gold Deposit ◽  
Ore Minerals ◽  
Ore Mineralization ◽  
Alteration Minerals ◽  
Homogenization Temperatures ◽  
Low Sulfidation

The Kyaukmyet prospect is one of the principal epithermal gold prospects in the Monywa District, Central Myanmar; its gold- and base metal-bearing quartz veins contain around 3 g/t gold. Ore minerals are mainly hosted by volcanic and volcaniclastic rocks of the Late Oligocene to Middle Miocene Magyigon Formation. The distribution of magmatic intrusions in the area is controlled by ENE-WSW trending faults; these faults are likely related to ore mineralization. Common ore minerals at the Kyaukmyet prospect include pyrite, sphalerite, galena, chalcopyrite, and electrum. They occur in mineralized crustiform-textured brecciated quartz veins and banded (colloform) and massive quartz veins. Mineralized rock is accompanied by silicification and propylitic and argillic alterations. The alteration mineral assemblages include quartz, adularia, calcite, chlorite, illite/smectite, sericite, and illite. Fluid inclusions in the quartz veins have homogenization temperatures ranging from 148 °C to 304 °C and salinities from 0.35 wt % to 2.75 wt % NaCl equiv. The quartz in the mineralized quartz veins was most likely precipitated at a depth ranges165-256 m below the paleosurface. The precipitation of gold at the Kyaukmyet prospect may have been formed by mixing large amounts of meteoric fluid with small amounts of magmatic fluid. The coexistence of liquid-rich and vapor-rich inclusions and presence of adularia and bladed calcite indicate that fluid boiling is caused the main mechanism of ore formation. The vein textures, ore mineral assemblages, alteration minerals and fluid inclusion data suggest that the Kyaukmyet prospect is a polymetallic low-sulfidation epithermal gold deposit.

scholarly journals Sphalerite Composition in Low- and Intermediate-Sulfidation Epithermal Ore Bodies from the Roșia Montană Au-Ag Ore Deposit, Apuseni Mountains, Romania

Minerals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 634
Author(s):  
Călin Gabriel Tămaș ◽  
Mădălina Paula Andrii ◽  
Réka Kovács ◽  
Sergiu Drăgușanu ◽  
Béatrice Cauuet
Keyword(s):  
Manganese Content ◽  
Ore Deposits ◽  
Ore Deposit ◽  
Apuseni Mountains ◽  
Epithermal Deposits ◽  
Epithermal Mineralization ◽  
Ore Bodies ◽  
Baia Mare ◽  
Low Sulfidation ◽  
Rosia Montana

We evaluated the significance of the iron and manganese content in sphalerite as a tool for distinguishing between low-sulfidation and intermediate-sulfidation epithermal deposits on the basis of new and previously published electron probe microanalyses data on the Roșia Montană epithermal ore deposit and available microchemical data from the Neogene epithermal ore deposits located in the Apuseni Mountains and Baia Mare region, Romania. Two compositional trends of the Fe vs. Mn content in sphalerite were delineated, a Fe-dominant and a Mn-dominant, which are poor in Mn and Fe, respectively. The overlapping compositional range of Fe and Mn in sphalerite in low-sulfidation and intermediate-sulfidation ores suggests that these microchemical parameters are not a reliable tool for distinguishing these epithermal mineralization styles.

Bismuth-bearing assemblages from the Northern Pennine Orefield

1996 ◽  
Vol 60 (399) ◽  
pp. 317-324 ◽  
Author(s):  
R. A. Ixer ◽  
B. Young ◽  
C. J. Stanley
Keyword(s):  
Qualitative Analysis ◽  
Fine Grained ◽  
Quartz Veins ◽  
The North ◽  
Data Form ◽  
Form Part ◽  
Native Bismuth ◽  
Monoclinic Pyrrhotite ◽  
Early Phases ◽  
And Tungsten

AbstractBismuthinite-bearing quartz veins from the Alston Block of the North Pennine Orefield are all close to, or above, the Rookhope and Tynehead cupolas of the buried Weardale Granite. They are uniform in composition and paragenesis and are earlier than the main fluorite-baryte-galena-sphalerite mineralization of the orefield. Rhythmical crystallization of quartz, chalcopyrite and minor pyrite is followed by fluorite-quartz-chalcopyrite-minor sphalerite-altered pyrrhotite mineralization. Early tin-bearing (up to 0.29 wt.% Sn) chalcopyrite encloses trace amounts of bismuthinite (Bi2S3), synchysite (CaREE(CO3)F2), argentopentlandite (Ag(FeNi)8S8) (close to being stoichiometric), pyrrhotite, cubanite and cosalite (Pb2Bi2S5), while early pyrite carries monoclinic pyrrhotite (close to Fe7S8) and tungsten-bearing cassiterite (up to 1.03 wt.% WO3). Bismuthinite is macroscopically visible and is associated with native bismuth and small, fine-grained, spherical aggregates that qualitative analysis suggests may be cosalite crystals. Synchysite and more rarely monazite, xenotime and adularia are intergrown with bismuthinite. These mineralogical data form part of the basis for an increasing awareness of the contribution of the Weardale Granite to the early phases of mineralization in the Alston Block.

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