K-Ar Ages of Volcanic Rocks and Gold-Bearing Quartz-Adularia Veins in the Bodie Mining District, Mono County, California

We present and evaluate lanthanide contents measured by inductively coupled plasma mass spectrometry (ICP-MS) in fluorite samples from the fluorite deposits in Zacualpan and Taxco mining districts in the south of Mexico. The information is used to distinguish different generations of fluorite, to establish a correlation between mineralization episodes and the wall rock nature, and to identify postdepositional processes.The total lanthanide content of the fluorites are variable, and early- stage fluorite samples are usually enriched in LREE. The concentration of REE in fluorite is low in comparison with the volcanic and metamorphic rocks (∑REE > 100 ppm) and is generally high respect the carbonates (∑REE < 30 ppm). There is host rock influence. The higher REE concentra- tions are in fluorites hosted by volcanic rocks. The fluorite that replaced carbonate is characterized by low REE to very low concentrations. Fluorite samples associated with sulfurs are typically enriched in HREE. Nearly all fluorites show a negative Eu anomaly similar to the REE anomaly observed in the volcanic rock. Only some early stage dark, uranium rich fluorites, from la Azul deposit, have a strong positive Eu anomaly. Direct correlation between color and REE patterns is observed in some samples.In the Zacualpan mining district, only an episode of mineralization has been discriminated, where fluorite presents flat to HREE- enriched chondrite-normalized REE patterns.In the Taxco mining district and particularly in the “Mina la Azul”, multiple hydrothermal events of mineralization have been determined. The first generation of fluorite is formed by replacement of carbonates and is characterized by very low contents of lanthanides, chondrite- normalized REE patterns similar to the limestone, high strontium content and primary textures (e.g. massive fluorite and rhythmites). The second generation of fluorite is related to the entry of new fluid to the system and has higher REE concentrations, chondrite-normalized REE patterns similar to volcanic rocks, low strontium content and secondary textures (i.e. breccias, nodules). Most of the samples show a genetic relationship between fluorite and fluids of magmatic origin.

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Geochemistry of Palaeoproterozoic volcanic rocks of the Iricoumé Group, Pitinga Mining District, Amazonian craton, Brazil

International Geology Review ◽

10.1080/00206810903391542 ◽

2009 ◽

Vol 53 (8) ◽

pp. 946-979 ◽

Cited By ~ 13

Author(s):

Ronaldo Pierosan ◽

Evandro Fernandes de Lima ◽

Lauro Valentin Stoll Nardi ◽

Artur Cesar Bastos Neto ◽

Cristina P. de Campos ◽

...

Keyword(s):

Volcanic Rocks ◽

Mining District ◽

Amazonian Craton

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Geochemistry and provenance of metasedimentary rocks from the Archean Golden Pond sequence (Casa Berardi mining district, Abitibi subprovince)

Canadian Journal of Earth Sciences ◽

10.1139/e96-051 ◽

1996 ◽

Vol 33 (5) ◽

pp. 676-690 ◽

Cited By ~ 10

Author(s):

M. R. Flèche ◽

G. Camiré

Keyword(s):

Chemical Weathering ◽

Volcanic Rocks ◽

Source Area ◽

Source Rocks ◽

Iron Formation ◽

Mining District ◽

Metasedimentary Rocks ◽

Clastic Rocks ◽

The North ◽

Volcanic Source

The Archean Golden Pond sequence is made up of deformed and metamorphosed conglomerates, greywackes, and mafic volcanic rocks, and is overlain by ferrugineous metasedimentary rocks of the North iron formation. The clastic rocks were derived mainly from a volcanic source that had undergone weak chemical weathering. Their source area was dominated by the presence of 60–80% high-Al2O3 felsic volcanics having strongly fractionated [La/Sm]N (= 3.7 ± 0.3) and very low Ta/Th ratios (= 0.09 ± 0.02), with lesser proportions of basaltic (10–30%) and ultramafic volcanic rocks (1–10%). The ferrugineous metasedimentary rocks can be modelled by mixing 20–40% siliciclastic material, of the composition of the average Golden Pond greywacke, with an Fe- and Si-rich precipitate (molecular Fe/Si = 0.6 ± 0.2). The high-Al2O3 felsic source rocks were most likely produced by subduction processes within an oceanic arc environment, but the mafic and ultramafic volcanic rocks were derived by different processes from an asthenospheric mantle source, possibly in an oceanic rift environment. Therefore, it is suggested that the ultramafic, mafic, and felsic volcanic rocks were brought to the same erosional level by dissection of the arc system and rapid exhumation of the felsic arc lithologies and the deeper ocean floor. Intrabasinal hydrothermal activity associated with contemporaneous mafic volcanism and (or) graben development may have also been responsible for the local production of the Fe-rich precipitates of the North iron formation.

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Structural geology of the Blake River Group at the Bousquet mine, Abitibi, Quebec

Canadian Journal of Earth Sciences ◽

10.1139/e88-056 ◽

1988 ◽

Vol 25 (4) ◽

pp. 581-592 ◽

Cited By ~ 6

Author(s):

Ghislain Tourigny ◽

Claude Hubert ◽

A. C. Brown ◽

Robert Crépeau

Keyword(s):

Gold Mineralization ◽

Volcanic Rocks ◽

Fault Zones ◽

Mining District ◽

Kink Bands ◽

Crenulation Cleavage ◽

Northern Half ◽

Volcaniclastic Rocks ◽

Volcanic Succession ◽

A Minor

In the Bousquet mining district, metamorphosed volcanic rocks of the Blake River Group (BRG) exhibit discrete strain features resulting from three generations of structures—D1, D2, and D3. Deformation D1 formed an east–west-trending, subvertical, penetrative schistosity that is coplanar with the axial plane of associated folds. This foliation contains a linear fabric plunging steeply westward, and mineral lineations are subparallel to fold axes and to intersection lineations.Defomations D2 and D3 formed a crenulation cleavage and a set of conjugate kink bands, respectively. The cleavage is oriented east–northeast, and the kink bands are oriented northeast–southwest and northwest–southeast. Both deformations distorted earlier-formed structures to a minor extent. A conjugate set of minor strike-slip faults with orientations similar to the kinks are the youngest structures found in BRG rocks.The volcanic sequence is composed of two lithotectonic domains juxtaposed along fault-related contacts. Each domain exhibits distinctive strain features attributed mainly to a broad network of anastomosing faults. This network of faults disrupted strata and destroyed many internal stratigraphic features, especially in domain 2; it relates to late stages of D1.Domain 1, occupying the northern half of the BRG in the mine area, represents a zone of weakly sheared tholeiitic basalts 750 m thick and is overlain by 150 m of felsic volcaniclastic rocks. Primary textures and structures indicate that this domain forms a south-facing homoclinal succession.Domain 2 is characterized by a strongly strained, 500 m wide belt of anastomosing faults adjacent to the southern margin of domain 1. Narrow bands of schist, mylonite, and phyllonite straddle fault zones and surround less-deformed, lozenge-shaped blocks of metamorphosed volcanic and (or) volcaniclastic rocks.The lack of syngenetic structures and textures, together with intense faulting and transposition, restricts stratigraphic correlations throughout the BRG as well as correlations between this volcanic succession and the adjacent sedimentary units. Structural evidence presented here complicates the original stratigraphic scheme commonly applied to volcano-sedimentary assemblages in the Rouyn–Val D'Or area. It is proposed that faulting is responsible for the spatial distribution of lithologies previously interpreted as resulting from folding phenomena in the Bousquet mining district. Gold mineralization is concentrated in bands of deformed rocks in the fault zones of domain 2 at the Bousquet mine.

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The geochemistry of gold-bearing chemical sediments, Dickenson Mine, Red Lake, Ontario: a reconnaissance study

Canadian Journal of Earth Sciences ◽

10.1139/e81-055 ◽

1981 ◽

Vol 18 (3) ◽

pp. 624-637 ◽

Cited By ~ 7

Author(s):

R. Kerrich ◽

B. J. Fryer ◽

K. J. Milner ◽

M. G. Peirce

Keyword(s):

Volcanic Rocks ◽

Hydrothermal Fluids ◽

Base Metals ◽

Sea Floor ◽

Red Lake ◽

Reconnaissance Survey ◽

Rare Elements ◽

Chemical Sediments ◽

Mobile Base ◽

Gold Bearing

Auriferous sedimentary rocks at the Dickenson Mine, Red Lake, are characterized by large enrichments of rare elements (Au, Ag, Pd, As, Sb, B) and metals conventionally considered to be relatively immobile (Ni, W), with negligible concentrations of the abundant and mobile base metals. Based on a reconnaissance survey involving 12 rocks analysed for 42 elements, these sediments can be represented in terms of a mixture of two components―mafic volcaniclastic material and hydrothermal precipitates. The volcaniclastic component has a composition closely comparable to mafic volcanic rocks that conformably envelope the sediments, and contributes all of the Al, Ti, V, Sc, Zr, and F. The hydrothermal component donates Si, Fe, Mn, Mg, Ca, K, Si, and C, together with Au, Ag, Pd, As, Sb, B, W, and Ni. Chromium and nickel are contributed from both sources. Alteration of the mafic volcanic rocks that envelope the auriferous sediments involved fixation of Si, K, and CO2, in contrast to the typical patterns of metasomatism in footwall rocks to base metal massive sulphide deposits, which are characterized by Mg, Fe (Si, S) addition.Quartz isolated from chert within the auriferous sediments and volcanic rocks has a maximum δ18O of 19‰, which is within the range of δ values for marine cherts of ~2.8 Ga, and signifies precipitation in equilibrium with ambient marine water of ~−1‰ at ~70–90 °C. Mafic volcanic wall rocks to the sediments have whole-rock δ18O values of 16–17‰ and Δquartz–chlorite ≤ 2‰. The anomalously heavy whole-rock isotopic composition and small quartz–chlorite fractionation may result from the growth of chlorite from precursors such as zeolites and smectite. Alternatively, chlorite or its precursors may have become enriched in 18O by isotope exchange with metamorphic hydrothermal fluids that become ponded when discharge to the hydrosphere was capped by overlying basalts.Rare earth element (REE) distributions in sediments and mafic volcanic wall rocks are characterized by relatively flat normalized patterns up to Sm–Gd, followed by an abrupt continuous decline in abundance. This implies modification of the primary tholeiitic abundances by hydrothermal solutions capable of mobilizing heavy REE's relative to light REE's. The environment that would satisfy the geological observations and chemical data is one of metamorphic hydrothermal fluids emmanating onto the sea floor during a period of relatively quiescent mafic submarine volcanism, with subsequent capping of the discharge during emplacement of the overlying pillow basalts.

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Geological setting of gold, western Wabigoon Subprovince, Canadian Shield: exploration targets in mixed volcanic successions

Canadian Journal of Earth Sciences ◽

10.1139/e88-192 ◽

1988 ◽

Vol 25 (12) ◽

pp. 2075-2088 ◽

Cited By ~ 3

Author(s):

David R. Melling ◽

Charles E. Blackburn ◽

David H. Watkinson ◽

Jack R. Parker

Keyword(s):

Volcanic Rocks ◽

Shear Zones ◽

Canadian Shield ◽

Field Mapping ◽

Geological Setting ◽

Intrusive Rocks ◽

Volcaniclastic Rocks ◽

Gold Bearing

The Archean volcanic rocks in the Cameron–Rowan lakes area may be divided into three distinct successions based on field mapping, petrographic studies, and lithogeochemical characteristics. The lowermost Rowan Lake Volcanics are tholeiitic pillowed basalts. These rocks are unconformably overlain by the Cameron Lake Volcanics, a mixed succession of tholeiitic massive and pillowed basalts and intermediate to felsic volcaniclastic rocks. The Brooks Lake Volcanics consist of tholeiitic basalts and represent the youngest volcanic rocks at the top of the preserved succession.Most of the gold concentrations in the Cameron–Rowan lakes area are confined to the mixed Cameron Lake Volcanics. The majority of these, including the Cameron Lake deposit, occur within shear zones near lithologic contacts. In the Eagle–Wabigoon and Manitou lakes areas there are similar stratigraphic subdivisions of the supracrustal rocks and many of the gold concentrations also occur in deformation zones within the mixed volcanic successions. The contrasting competencies among the basalts, the intermediate to felsic volcaniclastic rocks, and the intrusive rocks, which are characteristic of the mixed volcanic successions, localized stress during deformation, forming shear zones into which gold-bearing fluids gained access. The potential for successfully delineating economic gold concentrations appears greatest in the mixed volcanic successions within these areas and elsewhere in the western Wabigoon Subprovince of the Canadian Shield.

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Caractéristiques pétrographiques et géochimiques de la minéralisation aurifère à la mine Elder, Abitibi, Québec

Canadian Journal of Earth Sciences ◽

10.1139/e90-173 ◽

1990 ◽

Vol 27 (12) ◽

pp. 1637-1650 ◽

Cited By ~ 2

Author(s):

R. Gaulin ◽

P. Trudel

Keyword(s):

Earth Element ◽

Volcanic Rocks ◽

Reverse Fault ◽

Gold Content ◽

Mafic Dike ◽

Gold Mines ◽

Quartz Veins ◽

Gold Enrichment ◽

Main Vein ◽

Gold Bearing

The Elder deposit is located on the southeast border of the Flavrian Batholith, which intrudes the Blake River Group of archean volcanic rocks. The ore zone is composed of veins 1, 3, 5, and 4. The first three veins are a series of brecciated quartz veins having mean strike and dip of N72°E and 28°SE. Least important is vein 4, striking N20°W and dipping 28°NE. A reverse fault and a mafic dike are associated with the main vein 1, which occurs within trondhjemite in contact with hybrid rocks. The mafic dike represents an important metallotect. The ore zone is marked by abundant carbonates and pyrite, is slightly enriched in hematite and rutile, and is lightly depleted in sericite and chlorite. The mineralogical variation depends on CaO, MgO, CO2, S, TiO2, Fe2O3, MnO, and P2O5 enrichments and SiO2, Na2O, Al2O3, and H2Odepletions. A gold-bearing halo 8 m wide surrounds the ore zone. Seventy-nine per cent of the gold grains are associated with pyrite; otherwise gold occurs mostly as inclusions in the plagioclase matrix. Gold enrichment and rare-earth-element (REE) losses in the ore zone are similar to those observed in other Abitibi gold mines. In veins 1, 3, and 5, divergences in Ag and As enrichments, gold content, and REE concentrations suggest different ore-forming solutions.[Journal Translation]

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A new look at the stratigraphy of the Yellowknife Supergroup at Yellowknife, N.W.T. — implications for the age of gold-bearing shear zones and Archean basin evolution

Canadian Journal of Earth Sciences ◽

10.1139/e86-049 ◽

1986 ◽

Vol 23 (4) ◽

pp. 454-475 ◽

Cited By ~ 46

Author(s):

H. Helmstaedt ◽

W. A. Padgham

Keyword(s):

Volcanic Rocks ◽

Shear Zones ◽

Gold Deposits ◽

Spreading Center ◽

Group Status ◽

Slave Province ◽

Lake Formation ◽

Group A ◽

Sea Floor Spreading ◽

Gold Bearing

Based on recent detailed mapping, a revised stratigraphic column is proposed for the rocks of the Archean Yellowknife Supergroup in the Yellowknife greenstone belt. The mafic volcanic rocks of the Kam Formation, previously thought to represent the oldest supracrustal rocks of the belt, overlap remnants of an earlier volcanic–sedimentary sequence, here referred to as the Octopus Formation. As its enormous thickness makes it too unwieldy to be described as a single formation, the Kam Formation is raised to group status and subdivided into four formations. It is proposed that the Kam Group should replace the Beaulieu Group in the Yellowknife area. The Chan Formation, at the base of the Kam Group, consists of multiple gabbroic intrusions that were emplaced into a carapace of pillowed flows. The intrusions locally resemble sheeted mafic dyke complexes in Phanerozoic ophiolites, thought to represent evidence for sea-floor spreading. The Crestaurum Formation, which overlies the Chan Formation, is characterized by massive and pillowed flows interlayered with a number of laterally continuous cherts and felsic tuffs. The Townsite Formation consists of rhyodacite breccias interbedded with felsic tuffs and pillowed dacites. The Yellowknife Bay Formation, at the top of the Kam Group and comprising massive and pillowed flows with pillow breccias and numerous interflow sediments, contains all the important gold deposits mined at Yellowknife. The Banting Formation, directly overlying the Kam Group and consisting of mafic to felsic volcanics, is also given group status and subdivided into two formations. Conglomerates and sandstones of the Jackson Lake Formation, formerly thought to separate the Kam and Banting groups, are considered to represent the youngest rocks of the Yellowknife Supergroup near Yellowknife. Gold-bearing shear zones clearly postdate deposition of the Banting Group, making the rocks of this group a potential target for gold exploration. The presence of remnants of a possible spreading center at the base of the Kam Group suggests that plate-tectonic processes were active during the formation of Archean supracrustal basins in the Slave Province.

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