Occurrences of dendritic gold at the McLaughlin Mine hot-spring gold deposit

Sherlock, Ross; Lehrman, Norman J.

doi:10.1007/bf00196368

Cited by 23 publications

(8 citation statements)

References 14 publications

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“…Therefore, the dendritic aggregates of palladian gold appear to be only weakly affected by weathering, and are more likely residual components of a primary, hydrothermal mineralization. In this connection, it is worth mentioning that dendritic gold is known to occur in epithermal and hot-spring gold deposits (Saunders 1994, Sherlock & Lehrman 1995. Also, the dendritic aggregates of Pt-Pd and Pd-Hg-Au alloys from the Bom Sucesso stream, Minas Gerais, possibly result from open-space infill by low-temperature hydrothermal fluids (Cassedanne et al 1996, Fleet et al 2002.…”

Section: Dendrites Of Palladian Goldmentioning

confidence: 99%

PALLADIUM AND PLATINUM MINERALS FROM THE SERRA PELADA Au-Pd-Pt DEPOSIT, CARAJAS MINERAL PROVINCE, NORTHERN BRAZIL

Cabral

Lehmann

Kwitko-Ribeiro

et al. 2002

The Canadian Mineralogist

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The Serra Pelada garimpo (1980)(1981)(1982)(1983)(1984) was the site of the most spectacular gold rush in recent history, but the mineralogy of the bonanza-style mineralization has not so far been documented in detail. Rediscovery of an early drill-core, recovered in 1982 from the near-surface lateritic portion of the garimpo area, has provided coarse-grained gold aggregates for this study. The centimeter-long aggregates of gold occur in powdery, earthy material. They exhibit a delicate arborescent fabric and are coated by goethite. Four compositional types of gold are recognized: palladian gold with an atomic ratio Au:Pd of 7:1 ("Au 7 Pd"), Hgbearing palladian gold (Au-Pd-Hg), Pd-bearing gold with up to 3 wt.% Pd (Pd-poor gold) and pure gold. A number of platinumgroup minerals (PGM) are included in, or attached to the surface of, palladian gold: "guanglinite", Sb-bearing "guanglinite", atheneite and isomertieite, including the noteworthy presence of Se-bearing PGM (Pd-Pt-Se, Pd-Se, Pd-Hg-Se and Pd-Bi-Se phases, and sudovikovite and palladseite). They define an As-Sb-Hg-Se mineral assemblage typical of hydrothermal vein-type deposits formed at relatively low temperatures. Native palladium, characteristically situated in the goethite coating, is intimately associated with a Pd-O phase. The remarkable occurrence of native platinum associated with Pd-bearing gold, PGM (compositionally close to mertieite-II and isomertieite) and berzelianite from a nearby prospect (Elefante prospect) is also recorded.

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Section: Dendrites Of Palladian Goldmentioning

confidence: 99%

PALLADIUM AND PLATINUM MINERALS FROM THE SERRA PELADA Au-Pd-Pt DEPOSIT, CARAJAS MINERAL PROVINCE, NORTHERN BRAZIL

Cabral

Lehmann

Kwitko-Ribeiro

et al. 2002

The Canadian Mineralogist

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“…Although perhaps best evident in LS epithermal deposits from Nevada, Idaho, and Washington of the western USA such as those discussed here, gold/electrum nanoparticles might also be locally important in some bonanza epithermal ores such as in Japan [5][6][7][8][9][10] and elsewhere in western USA such as McLaughlin, California [26], and the Sunnyside gold mine [46] of the Silverton district, San Juan Mountains, Colorado. High-grade Sunnyside ores contained discrete electrum/gold-rich depositional events that also appear to have formed by colloid aggregation (Figure 9).…”

Section: Discussionmentioning

confidence: 99%

“…Thus in the newer terminology those "fractal" dendrites were made from electrum nanoparticles as opposed to colloids. Others have interpreted the origin of "fractal" dendrites in bonanza epithermal gold ore to be the result of diffusion of gold in silica gels [26]. Do gold (or naumannite) nanoparticles have different physical properties than gold colloids, and do nanoparticles of gold as they are transported up?…”

Section: Introductionmentioning

confidence: 99%

Textural Evidence of Episodic Introduction of Metallic Nanoparticles into Bonanza Epithermal Ores

Saunders

2012

Minerals

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Tertiary low sulfidation (LS) epithermal deposits in the western USA often show evidence of the former presence of nanoparticle-sized precious-metal and silica phases in the highest grade (bonanza) ores. Here, nanoparticles are defined to have a size less than ~10 −7 m. The ore-mineral textures that formed from aggregation of nanoparticles (or colloids) observed to date in these ores include electrum and naumannite (Ag 2 Se). Here it is proposed that chalcopyrite also forms nanoparticles in these ores, but sulfide nanoparticles apparently have significantly different physical (surface) properties than the precious-metal phases, and thus exhibit different mineral textures (e.g., no textural evidence of previous chalcopyrite nanoparticles). Textures described here show that nanoparticles of precious-metal phases and silica were episodically and often repeatedly deposited to form the banded bonanza veins typical of many western USA epithermal deposits. Chalcopyrite is the most abundant metal-sulfide mineral in these bonanza ores, and it was also deposited episodically as well, and it appears to replace earlier formed naumannite dendrites. However, this apparent "replacement" texture may just be the result of naumannite dendrite limbs trapping chalcopyrite nanoparticles that later recrystallized to the apparent replacement texture. The episodic and repetitive nature of the metal-depositing events may record periodic "degassing" of magma chambers at depth, where metals are repeatedly delivered to the shallow epithermal environment by "vapor-phase" metal (loid) transport.

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“…In contrast to this colloform quartz, bands composed of other textural types of quartz are barren. Similarly, Sherlock and Lehrman [76] demonstrated that colloform bands in crustiform veins from the McLaughlin deposit in California consist of compacted microspheres of quartz that formed through recrystallization of a noncrystalline silica precursor phase. The bands contain gold as dendrites or as particles that are concentrated in the interstitial space between the microspheres.…”

Section: Implications For Ore-forming Processesmentioning

confidence: 91%

“…Fluid inclusion evidence from Buckskin National in Nevada [40,42], Sleeper in Nevada [79], McLaughlin in California [76,80], Guanajuato in Mexico [14,81], and Koryu in Japan [17] is interpreted to indicate that phase separation of the hydrothermal liquids occurred during vein formation, even though the exact conditions of noncrystalline silica deposition cannot be ascertained due to the lack of primary fluid inclusions in the colloform bands composed of relic microspheres. Additional evidence for the occurrence of boiling at these deposits includes the presence of platy calcite which is replaced by quartz pseudomorphs (cf.…”

Section: Implications For Ore-forming Processesmentioning

confidence: 99%

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

Taksavasu

Monecke

Reynolds³

2018

Minerals

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Abstract: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.

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Occurrences of dendritic gold at the McLaughlin Mine hot-spring gold deposit

Cited by 23 publications

References 14 publications

PALLADIUM AND PLATINUM MINERALS FROM THE SERRA PELADA Au-Pd-Pt DEPOSIT, CARAJAS MINERAL PROVINCE, NORTHERN BRAZIL

PALLADIUM AND PLATINUM MINERALS FROM THE SERRA PELADA Au-Pd-Pt DEPOSIT, CARAJAS MINERAL PROVINCE, NORTHERN BRAZIL

Textural Evidence of Episodic Introduction of Metallic Nanoparticles into Bonanza Epithermal Ores

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

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