scholarly journals Crustal-scale transport of nanoparticle emulsion forms ore deposits

2021 ◽  
Author(s):  
Laura Petrella ◽  
Nicolas Thebaud ◽  
Denis Fougerouse ◽  
Laure Martin ◽  
Stephen Turner ◽  
...  
Keyword(s):  
Metal Nanoparticles ◽  
Colloidal Silica ◽  
Ore Deposits ◽  
Step Change ◽  
Hydrothermal Fluids ◽  
Low Density ◽  
Upper Crust ◽  
Fold Enrichment ◽  
Nanoparticle Suspensions ◽  
Accumulation Of Metals

Abstract A 10- to 10 000-fold enrichment is required to form economic metal deposits. Such enrichment is achieved through the accumulation of metals transported in hydrothermal fluids from their source to the deposit. The contribution of gold nanoparticle suspensions in fluids is required to form bonanza gold grades. However, as the source of gold is spatially disconnected from the deposit location, it is not known how the transport of gold nanoparticles is achieved. Here we show that metal nanoparticles (Au, AgO, AuAg Cu) are stabilised by colloidal silica in nanoparticle emulsion and transported with the aid of low-density carbonic phases. We document systematic occurrence of metals nanoparticle in five deposits that show a previously unrecognized association with amorphous silica and carbon. Our results demonstrate that stabilisation of metal nanoparticles may be achieved over kilometres through the Earth’s upper crust and offers a step change in our understanding of metalliferous deposit formation.

Formation of coagulated colloidal silica in high-temperature mineralizing fluids

2002 ◽  
Vol 66 (4) ◽  
pp. 547-553 ◽  
Author(s):  
B. J. Williamson ◽  
J. J. Wilkinson ◽  
P. F. Luckham ◽  
C. J. Stanley
Keyword(s):  
High Temperature ◽  
Hydrothermal Fluid ◽  
Colloidal Silica ◽  
Fluid Transport ◽  
Experimental Studies ◽  
Hydrothermal Fluids ◽  
Ore Formation ◽  
Colloidal Gel ◽  
Material Forming ◽  
Mineralizing Fluids

AbstractRecent experimental studies have suggested that colloidal silica can form in high-T (300 to >700°C) hydrothermal fluids (Wilkinson et al., 1996). Natural evidence in support of this was found by Williamson et al. (1997) who proposed a colloidal (gel) silica origin for <50 μm irregularly-shaped inclusions of quartz contained in greisen topaz from southwest England. Confocal and microprobe studies, presented here, strengthen this argument although rather than forming a gel in the hydrothermal fluid, it is suggested that the colloidal silica aggregated as a viscous coagulated colloid, with much of its volume (<10 to 30 vol.%) consisting of metal (mainly Fe) -rich particles. This is evident from the largely solid nature of metal-rich shrinkage bubbles contained at the margins of the inclusions of quartz which shows that the material forming the inclusions contained much less liquid than would be expected in a silica gel. These findings may have important implications for models of ore formation since the precipitation of a coagulated colloid could inhibit hydrothermal fluid transport and cause co-deposition of silica and entrained ore-forming elements. The mode of formation of the colloidal silica and further implications of the study are discussed.

Magmatic-Hydrothermal Fluids

Elements ◽  
2020 ◽  
Vol 16 (6) ◽  
pp. 401-406 ◽  
Author(s):  
Andreas Audétat ◽  
Marie Edmonds
Keyword(s):  
Metal Content ◽  
Fluid Phase ◽  
Volcanic Eruptions ◽  
Hydrothermal Systems ◽  
Ore Deposits ◽  
Hydrothermal Fluids ◽  
Geological Processes ◽  
Mineral Growth ◽  
Fluid Saturation ◽  
Fluid Phase Equilibria

Magmatic-hydrothermal fluids play a key role in a variety of geological processes, including volcanic eruptions and the formation of ore deposits whose metal content is derived from magmas and transported to the site of ore deposition by means of hydrothermal fluids. Here, we explain the causes and consequences of fluid saturation in magmas, the corresponding fluid-phase equilibria, and the behavior of metals and ligands during the transition from magma to an exsolved hydrothermal fluid. Much of what we know about magmatic-hydrothermal systems stems from the study of fluid inclusions, which are minute droplets of fluids trapped within minerals during mineral growth.

scholarly journals Elevated magma fluxes deliver high-Cu magmas to the upper crust

Geology ◽  
2020 ◽  
Vol 48 (10) ◽  
pp. 957-960
Author(s):  
Daniel Cox ◽  
Sebastian F.L. Watt ◽  
Frances E. Jenner ◽  
Alan R. Hastie ◽  
Samantha J. Hammond ◽  
...  
Keyword(s):  
Small Proportion ◽  
Ore Deposits ◽  
Crustal Evolution ◽  
Upper Crust ◽  
Convergent Margins ◽  
Ore Genesis ◽  
Porphyry Cu ◽  
Show Evidence ◽  
Lower Crustal ◽  
Garnet Fractionation

Abstract Porphyry Cu-Au ore deposits are globally associated with convergent margins. However, controls on the processing and distribution of the chalcophile elements (e.g., Cu) during convergent margin magmatism remain disputed. Here, we show that magmas feeding many Chilean stratovolcanoes fractionate sulfides with a high-Cu/Ag ratio early in their crustal evolution. These magmas show evidence of lower-crustal garnet and amphibole crystallization, and their degree of sulfide fractionation and Cu depletion increase with both crustal thickness and the extent of garnet fractionation. However, samples from a small proportion of volcanoes with elevated eruptive fluxes depart from this Cu-depleting trend, instead erupting Cu-rich magmas. This implies that at these atypical sites, elevated magma productivity and crustal throughput, potentially facilitated by “pathways” exploiting major crustal fault systems, enable rapid magma transit, avoiding lower-crustal Cu-depleting sulfide fractionation and potentially playing an important role in porphyry ore genesis.

scholarly journals Structural Controls of Ore Mineralization in a Polydeformed Basement: Field Examples from the Variscan Baccu Locci Shear Zone (SE Sardinia, Italy)

Minerals ◽  
2018 ◽  
Vol 8 (10) ◽  
pp. 456 ◽  
Author(s):  
Antonio Funedda ◽  
Stefano Naitza ◽  
Cristina Buttau ◽  
Fabrizio Cocco ◽  
Andrea Dini
Keyword(s):  
Shear Zone ◽  
Hanging Wall ◽  
Ore Deposits ◽  
Hydrothermal Fluids ◽  
Orogenic Gold ◽  
Mine Area ◽  
Structural Controls ◽  
Mylonitic Foliation ◽  
Ore Mineralization ◽  
Ore Mineralogy

The Baccu Locci mine area is located in a sector of the Variscan Nappe zone of Sardinia (the Baccu Locci shear zone) that hosts several type of ore deposits mined until the first half of the last century. The orebodies consist of lenses of Zn–Cu sulphides, once interpreted as stratabound, and Qtz–As–Pb sulphide ± gold veins; the implication of structural controls in their origin were previously misinterpreted or not considered. Detailed field mapping, structural analyses, and ore mineralogy allowed for unraveling how different ore parageneses are superimposed each other and to recognize different relationships with the Variscan structures. The sulphide lenses are parallel to the mylonitic foliation, hosted in the hinges of minor order upright antiforms that acted as traps for hydrothermal fluids. The Qtz–As–Pb sulphide veins crosscut the sulphide lenses and are hosted in large dilatational jogs developed in the hanging wall of dextral-reverse faults, whose geometry is influenced by the attitude of reverse limbs of late Variscan folds. The ores in the Baccu Locci shear zone are best interpreted as Variscan orogenic gold-type; veins display mutual crosscutting relationships with mafic dikes dated in the same district at 302 ± 0.2 Ma, a reliable age for the mineralizing events in the area.

Fe solubilities in very saline hydrothermal fluids; their relation to zoning in some ore deposits

1986 ◽  
Vol 81 (2) ◽  
pp. 447-465 ◽  
Author(s):  
T. A. P. Kwak ◽  
W. M. Brown ◽  
P. B. Abeysinghe ◽  
Teong Hing Tan
Keyword(s):  
Ore Deposits ◽  
Hydrothermal Fluids

scholarly journals Paleo heat flow in areas of Sedimentary Exhalative (SEDEX) deposits of Eastern Brazil

2019 ◽  
Vol 2 (1) ◽  
pp. 11-16
Author(s):  
Sundaram Iyer ◽  
Valiya Hamza
Keyword(s):  
Heat Flow ◽  
High Heat ◽  
Ore Deposits ◽  
Upper Crust ◽  
High Heat Flow ◽  
Radiogenic Heat ◽  
Sulphide Ore ◽  
Production Values ◽  
Eastern Brazil ◽  
Short Period

Representative values of fluid inclusion temperatures and radiogenic heat production values have been compiled as part of an attempt to determine paleo heat flow in areas sedimentary exhalative (SEDEX) deposits in thirteen localities of eastern Brazil. The results obtained indicate heat flow in excess of 80 mW/m2in areas of mineral bearing sulphide ore deposits, during periods of ore forming processes. Such anomalously high heat flow are more than twice the present-day values for stable tectonic units of Precambrian age. There are indications that high heat flow values were sustained by circulation of hydrothermal fluids in the upper crust, during periods not exceeding a few hundred million years. The resulting geothermal episodes may be considered as constituting short-period “heat pulses” occurring in stable tectonic environments, generated by magma emplacements in the upper crust, leading to formation of areas of sulfide ore deposits. Model simulations indicate that subsidence episodes induced by stretching and magma under-plating constitute the mechanisms for high heat flow during the ore-forming processes.

Hydrothermal Fluids

1996 ◽  
Author(s):  
Craig M. Bethke
Keyword(s):  
Hot Springs ◽  
Geochemical Modeling ◽  
Ore Deposits ◽  
Hydrothermal Fluids ◽  
Mississippi Valley ◽  
Midocean Ridges ◽  
First Case ◽  
Modeling Software ◽  
Geochemical Models ◽  
Ore Deposition

Hydrothermal fluids, hot groundwaters that circulate within the Earth’s crust, play central roles in many geological processes, including the genesis of a broad variety of ore deposits, the chemical alteration of rocks and sediments, and the origin of hot springs and geothermal fields. Many studies have been devoted to modeling how hydrothermal fluids react chemically as they encounter wall rocks, cool, boil, and mix with other fluids. Such modeling proliferated in part because hydrothermal fluids are highly reactive and because the reaction products are commonly well preserved, readily studied, and likely to be of economic interest. Further impetus was provided by the development of reliable modeling software in the 1970s, a period of concern over the availability of strategic and critical minerals and of heightened interest in economic geology and the exploitation of geothermal energy. As a result, many of the earliest and most imaginative applications of geochemical modeling, beginning with Helgeson’s (1970) simulation of ore deposition in hydrothermal veins and the alteration of nearby country rock, have addressed the reaction of hydrothermal fluids. For example, Reed (1977) considered the origin of a precious metal district; Garven and Freeze (1984), Sverjensky (1984, 1987), and Anderson and Garven (1987) studied the role of sedimentary brines in forming Mississippi Valley-type and other ore deposits; Wolery (1978), Janecky and Seyfried (1984), Bowers et al. (1985), and Janecky and Shanks (1988) simulated hydrothermal interactions along the midocean ridges; and Drummond and Ohmoto (1985) and Spycher and Reed (1988) modeled how fluid boiling is related to ore deposition. In this chapter, we develop geochemical models of two hydrothermal processes: the formation of fluorite veins in the Albigeois ore district and the origin of “black smokers, ” a name given to hydrothermal vents found along the ocean floor at midocean ridges. As a first case study, we borrow from the modeling work of Rowan (1991), who considered the origin of fluorite (CaF2) veins in the Albigeois district of the southwest Massif Central, France. Production and reserves for the district as a whole total about 7 million metric tons, making it comparable to the more famous deposits of southern Illinois and western Kentucky, USA.

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