Chemical changes during alteration of volcanic rocks and gold ore formation, La Libertad, Nicaragua

1991 ◽  
Vol 4 (1-2) ◽  
pp. 87-97 ◽  
Author(s):  
M. Darce ◽  
B. Levi ◽  
J.O. Nyström
Keyword(s):  
Volcanic Rocks ◽  
Ore Formation ◽  
Chemical Changes ◽  
Gold Ore

Mineralogy and textural relationships of ores from the Whalesback Mine, northeastern Newfoundland

1968 ◽  
Vol 5 (6) ◽  
pp. 1387-1395 ◽  
Author(s):  
K. Kanehira ◽  
D. Bachinski
Keyword(s):  
Shear Zone ◽  
Volcanic Rocks ◽  
Sulfide Deposit ◽  
Ore Formation ◽  
Pillow Lavas ◽  
Bay Area ◽  
Internal Reaction ◽  
Sulfide Ore ◽  
Ore Minerals ◽  
Pressure Shadow

The Whalesback Mine is one of many copper deposits associated with Ordovician volcanic rocks in the Notre Dame Bay area, Newfoundland. The deposit consists of veins, pods, and disseminated sulfides localized within a highly chloritized shear zone cutting basaltic pillow lavas. Porphyritic dikes cut the shear zone, sulfide deposit, and the surrounding pillow lavas; all of the rocks, including the sulfide-rich rocks, have been regionally metamorphosed. Ore minerals, in decreasing order of abundance, include pyrite, chalcopyrite, pyrrhotite, sphalerite, mackinawite, pentlandite, magnetite, cubanite, galena, and ilmenite. Marcasite, covellite, and goethite are supergene minerals. Chlorite and quartz are the predominant gangue minerals. Muscovite, carbonates, sphene, albite, and epidote are minor constituents. Banding and streaking of sulfides in massive ores, crushed pyrite, and the local occurrence of pressure-shadow phenomena in the ore are indicative of shearing stress post-dating original sulfide ore formation. Present sulfide assemblages are compatible with relatively low temperatures and are the result of re-equilibration and internal reaction among the sulfides with decreasing temperature.

scholarly journals SILVER-GOLD FORMATION TYPE ORE MINERALIZATION IN TAJIKISTAN

2018 ◽  
Author(s):  
Ф.А. Файзиев ◽  
А.Р. Файзиев
Keyword(s):  
Silver Sulfide ◽  
Ore Formation ◽  
Gold Ore ◽  
Quartz Veins ◽  
Multi Stage ◽  
Ore Minerals ◽  
Ore Mineralization ◽  
Formation Type ◽  
High Silver ◽  
Subsurface Formation

Серебро-золоторудный формационный тип минерализации в Таджикистане известен в пределах Табошар-Канджольского рудного узла (Карамазар) и на Памире. В Карамазаре к этому типу относятся месторождения Школьное, Четсу и Караулхона, а на Памире рудопроявления Сассык, Лянгар, Бугучиджилга, Курустык и др. Серебро-золоторудный формационный тип представлен убогосульфидными кварц-золоторудными жилами с высоким содержанием серебра. Рудные минералы представлены пиритом, тетраэдритом, халькопиритом, пираргиритом, фрейбергитом, миаргиритом, самородным золотом, электрумом и кюстелитом. Формационными особенностями этого типа являются предрудная пропилитизация, синрудная березитизация, многостадийный характер минерализации, простой минеральный состав, крайне неравномерное распределение серебра и золота, а также близповерхностное образование золота и его низкопробность. Продуктивное оруденение в них образовалось при сравнительно низких температурах (300–150ο) и давлениях (500 бар и ниже). Silver-gold ore-formation type mineralization in Tajikistan known within Taboshar-Kanjol – ore unit (Karamazar) and the Pamirs. The most known deposits KaramazarScholnoe, Chetsy and Karaulhona and the Pamirs to this type of ore can be attributed Sassyk, Langar, Buguchidzhilga, Kurustyk. Silver-gold ore-formation type is represented by poorly-high silver sulfide-quartz veins of gold mining. The ore minerals are pyrite, tetrahedrite, chalcopyrite, pyrargyrite, freibergite, miargyrite, native gold, electrum and kyustelitе. Formational peculiarities of this type are pre-ore propylitization, sin-ore beresitization, multi-stage nature of the mineralization, simple mineral composition, extremely uneven distribution of silver and gold, as well as subsurface formation of gold and its sleaze. Productive mineralization formed there in at relatively low temperatures (300–150ο) and pressures (500 bar or less).

Water in quartz as the indicator of intensity of hydrothermal ore formation: gold ore deposits

2016 ◽  
Vol 37 ◽  
pp. 65-73
Author(s):  
Е.А. Kalinichenko ◽  
◽  
А.B. Brik ◽  
А.М. Kalinichenko ◽  
A.A. Yushin ◽  
...  
Keyword(s):  
Ore Deposits ◽  
Ore Formation ◽  
Gold Ore

Petrochronology resolves the multi-Myr crustal scale magmatic evolution of an arc segment resulting in porphyry copper formation

2020 ◽  
Author(s):  
Simon Large ◽  
Yannick Buret ◽  
Tom Knott ◽  
Jamie Wilkinson
Keyword(s):  
San Francisco ◽  
Subduction Zones ◽  
Porphyry Copper ◽  
Empirical Studies ◽  
Volcanic Rocks ◽  
Geochemical Evolution ◽  
Magma Source ◽  
Magmatic Evolution ◽  
Ore Formation ◽  
The North

<p>The crustal-scale magmatic systems of Andean-style subduction zones produce thick volcanic deposits and abundant plutons emplaced into the upper crust. They can also result in the formation of spatially- and temporally-restricted, economically-important porphyry Cu deposits. Understanding the magmatic and tectonic processes acting within an arc segment, including changes in the fractionating assemblage, subduction angle, chemistry of slab-derived melts or water content, is essential to develop and refine quantitative models for the formation of these deposits. Specific geochemical signatures (e.g. elevated Sr/Y) are associated with magmas that source the metals and volatiles to form porphyry deposits based on empirical studies. However, it is unclear whether this geochemical signature is the result of geologically rapid processes resulting in sudden shifts in magma chemistry or whether they are the result of protracted changes within the crustal-scale magmatic system over extended timescales.</p><p>In this study we examine the magmatic evolution of the Rio Blanco-Los Bronces district, ~30 km northeast of Santiago, Chile, which is host to the Earth’s largest resource of Cu. Eocene to Early Miocene volcanic rocks were intruded by the Miocene San Francisco Batholith that, in turn, partially hosts intrusions related to the Late Miocene to Early Pliocene Rio Blanco-Los Bronces porphyry deposit cluster. We apply a combination of whole-rock and zircon geochemistry, isotopic tracing and LA-ICP-MS U-Pb geochronology to the intrusive rock suite of the district to provide temporally- constrained geochemical information over the entire duration of batholith assembly and ore formation.</p><p>U-Pb geochronology reveals incremental assembly of the San Francisco Batholith by individual magma batches over >13Myr (~17 – 4 Ma), with ore formation occurring in discrete pulses in the last 3 Myr before cessation of intrusive activity within the district. Temporally-resolved whole-rock major element chemistry shows that the progressively-emplaced magmas were not sourced from a common, continuously differentiating, lower crustal magma reservoir. Evolving trace element signatures over the recorded timescale indicate that magmas were sourced from progressively deeper fractional crystallisation reservoir(s) that exhibited increasing water contents. The geochemical evolution recorded over the entire investigated 13 Myr timescale could reflect geodynamic changes linked to the ingression of the subducting Juan Fernandez ridge from the north. However, within this continuous evolution, the most prominent geochemical shifts occur over a much shorter timescale of a few Myr, directly preceding economic ore-formation, implicating an additional mechanism for controlling the metallogenic potential of the magma source.</p><p> </p><p> </p><p> </p>

Resolving changes in arc magma volatile budgets over Myr timescales leading up to porphyry Cu formation 

2021 ◽  
Author(s):  
Simon Large ◽  
Chetan Nathwani ◽  
Yannick Buret ◽  
Tom Knott ◽  
Jamie Wilkinson
Keyword(s):  
San Francisco ◽  
Volcanic Rocks ◽  
Crustal Thickening ◽  
Ore Formation ◽  
Temporal Shift ◽  
Porphyry Deposit ◽  
Porphyry Cu ◽  
Entire Duration ◽  
Intrusive Activity ◽  
Rock Suite

<p>The crustal-scale magmatic systems of Andean-style arcs produce thick volcanic deposits and abundant plutons that are emplaced into the crust. They can also generate spatially- and temporally-restricted, economically-important porphyry Cu deposits. These deposits are formed at the magmatic-hydrothermal transition and require significant amounts of volatiles and metals to be concentrated in the sub-volcanic environment. Thus, understanding the magmatic and tectonic processes acting within an arc segment and their effect on the volatile budgets of crustal magmas could be essential for identifying the constraining factors controlling the potential of a magmatic system to produce a porphyry deposit.</p><p>In this study we examine the magmatic evolution of the Rio Blanco-Los Bronces district, ~30 km northeast of Santiago, Chile, which is host to the Earth’s largest resource of Cu. Eocene to Early Miocene volcanic rocks were intruded by the Miocene San Francisco Batholith that, in turn, partially hosts intrusions related to the Late Miocene to Early Pliocene Rio Blanco-Los Bronces porphyry deposit cluster. We apply a combination of whole-rock, apatite and zircon geochemistry and zircon geochronology to the intrusive rock suite of the district to provide temporally- constrained geochemical information over the entire duration of batholith assembly and ore formation.</p><p>U-Pb geochronology reveals incremental assembly of the San Francisco Batholith by individual magma batches over >14Myr (~18 – 4 Ma), with ore formation occurring in discrete pulses in the last 3 Myr before cessation of intrusive activity within the district. Progressive changes in the trace element chemistry indicate crustal thickening and deeper magma evolution within the arc segment as a result of the subduction of the Juan Fernandez ridge. A temporal shift to elevated SO<sub>3</sub> and Cl contents is recorded by zircon-hosted apatite inclusions from the intrusions with highest values occurring in porphyry intrusions directly associated with the ore forming events. These data suggest variable volatile budgets of magmas during zircon crystallisation and hint at crustal-scale controls on the porphyry ore-forming potential of an arc segment.</p><p> </p>

SPATIOTEMPORAL AND GENETIC RELATIONSHIPS OF GOLD ORE AND MERCURY-ANTIMONY MINERALIZATION AT THE HG-SB-GOLD-BEARINGCHAUVAI DEPOSIT (KIRGHIZIA): GEOLOGY, MINERALOGY OF ORES AND FEATURES OF HYDROTHERMAL-METASOMATIC PROCESSES

2021 ◽  
pp. 61-82
Author(s):  
A. V. Malyutina ◽  
◽  
Yu. O. Redin ◽  
A. S. Gibsher ◽  
V. P. Mokrushnikov ◽  
...  
Keyword(s):  
Mineral Composition ◽  
Gold Mineralization ◽  
Genetic Relationships ◽  
Ore Formation ◽  
Invisible Gold ◽  
Gold Ore ◽  
Terrigenous Rocks ◽  
Tectonic Contact ◽  
Instrumental Methods ◽  
High Arsenic

The Chauvai Hg-Sb deposit is a striking example of combining two contrasting types of mineralization in space: mercury-antimony and gold ones. The article studies the spatial-temporal and genetic relationships of goldore and mercury-antimony mineralization based on a complex of both traditional geological and mineralogicalgeochemical methods, as well as modern instrumental methods for analyzing the mineral composition. Two types of ores with clear structural confinedness have been found at the deposit: a) mercury-antimonic (cinnabarantimonite) ores, associated with jasperoid breccias and manifested exclusively along the tectonic contact of limestone of the Alai section and terrigenous rocks of the Tolubai Formation, and b) gold- sulphide (arsenopyritepyritic) ores, localized in slightly modified carbonate-terrigenous rocks of the Tolubai Formation, overlying the plane of tectonic contact. Ore formation occurred during the following stages: in the late diagenetic, without interruption passing into the catagenetic-hydrothermal, characterized by the formation of gold mineralization, and then in the later hydrothermal-telethermal, characterized by the development of Hg-Sb mineralization. It is established that the main carrying agent of invisible gold (“invisible gold”) in ores is framboidal and idiomorphic pyrite and, especially, its high-arsenic varieties. A set of conducted studies has shown that the gold ore and mercury-antimony mineralization is broken in time and is genetically associated with various hydrothermalmetasomatic processes, and the Chauvai deposit can be classified as a Carlin-like type.

scholarly journals Characteristics of fluid inclusions in the Cenozoic volcanic-hosted Kushk-e-Bahram Manto-type Cu deposit of central Iran

Geologos ◽  
2020 ◽  
Vol 26 (2) ◽  
pp. 127-137
Author(s):  
Marjan Jebeli ◽  
Peyman Afzal ◽  
Mohsen Pourkermani ◽  
Alireza Jafarirad
Keyword(s):  
Volcanic Rocks ◽  
Central Iran ◽  
Fluid Density ◽  
Two Phase ◽  
Ore Formation ◽  
Magmatic Arc ◽  
Density Values ◽  
Phase Liquid ◽  
Homogenization Temperatures ◽  
Volcanic Belts

AbstractThe Kushk-e-Bahram Manto-type Cu deposit is located in central Iran, within Eocene to Oligo–Miocene volcanic strata which occur in the central part of the Uremia-Dokhtar Magmatic Arc (UDMA). Propylitization, silicification, argillization and carbonatization are the main types of alteration to have affected the pyroclastic and volcanic rocks. There are high amounts of oxide minerals, including malachite, azurite, hematite, magnetite and goethite. Three types of primary FIs have been determined in the Kushk-e-Bahram deposit, namely; I: two-phase liquid-rich FIs (L+V), II: mono-phase liquid FIs, III: two-phase vapour-rich FIs which have been identified based on petrographical studies. Based on FI studies of co-existing quartz and calcite, homogenization temperatures (Th) must have been between 67 and 228°C, with an average of 158°C. Moreover, salinity is between 14.0–30.3 wt% NaCl, equivalent to a 19.6% average. Fluid density values vary from 0.8 to 1.1 gr/cm3. Based on FI data and related diagrams, the depth of their trapping was estimated to be <200 m and ore formation occurred at pressures of <50 bars. Consequently, mineralogy, host rock and FIs characteristics in the Kushk-e-Bahram deposit are similar to the Manto-type Cu deposits in Mesozoic-Cenozoic volcanic belts of Iran and South America.

scholarly journals AGE CONSTRAINTS AND METALLOGENIC PREDICTION OF GOLD DEPOSITS IN THE AKZHAL-BOKO-ASHALIN ORE ZONE (ALTAI ACCRETION-COLLISION SYSTEM)

2021 ◽  
Vol 12 (2) ◽  
pp. 392-408
Author(s):  
Yu. A. Kalinin ◽  
K. R. Kovalev ◽  
A. N. Serdyukov ◽  
A. S. Gladkov ◽  
V. P. Sukhorukov ◽  
...  
Keyword(s):  
Gold Mineralization ◽  
Gold Deposits ◽  
Igneous Rocks ◽  
Isotope Geochronology ◽  
Ore Formation ◽  
Gold Ore ◽  
Ore Mineralization ◽  
East Kazakhstan ◽  
Age Constraints ◽  
Gold Bearing

We present new age constraints for igneous rocks and ore-metasomatic formations of the gold deposits in the Akzhal-Boko-Ashalin ore zone. In terms of their ore formation, these deposits correspond mainly to the orogenic type, which generally reflects specific metallogeny of the West Kalba gold-bearing belt in East Kazakhstan. Gold-quartz veins and mineralized zones of the gold-sulphide formation are confined to fractures feathering regional NW-striking and sublatitudinal faults. Their common features include the following: gold-bearing veinlet-disseminated pyrite-arsenopyrite ores that are localized in carbonaceous-sandy-schist and turbidite strata of different ages; structural-tectonic control of mineralization, numerous dikes of medium-basic compositions in ore-control zones; and the presence of post-orogenic heterochronous granite-granodiorite rocks, although their relation to gold-ore mineralization is not obvious. Igneous rocks of the study area have similar ages in a narrow range from 309.1±4.1 to 298.7±3.2 Ma, which is generally consistent with the previously determined age of granitoid massifs of gold-ore fields in East Kazakhstan. A younger age (292.9±1.3 to 296.7±1.6 Ma) is estimated for felsic rocks of the dyke complex. For the ore mineralization, the 40Ar/39Ar dating of sericite from near-ore metasomatites yields two age intervals, 300.4±3.4 Ma and 279.8±4.3 Ma. A gap between of the ages of the ore mineralization and the igneous rocks is almost 20 Ma, which may indicate that the processes of ore formation in the ore field continued in an impulse-like pattern for at least 20 Ma. Nevertheless, this confirms a relationship between the hydrothermal activity in the study area and the formation and evolution of silicic igneous rocks of the given age interval, which belong to the Kunush complex, according to previous studies. This interpretation is supported by reconstructed tectonic paleostress fields, showing that directions of the main normal stress axes changed during the ore mineralization stage, which is why the ore bodies significantly differ in their orientations. The above-mentioned data are the first age constraints for the study area. Additional age determinations are needed to further improve understanding of the chronology of ore-forming processes. Actually, all the features characterizing the gold mineralization of the Akzhal, Ashalin and Dauba ore fields, including the data on lithology, stratigraphy, structural tectonics, magmatism, isotope geochronology, mineralogy and geochemistry, can be used as criteria when searching for similar ore fields in East Kazakhstan.

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