EFFECT OF ORGANIC MATTER ON AQUEOUS TRANSPORT OF COPPER AND ZINC FROM ORE DEPOSITS

Reflectance measurements and organic petrography were used to study altered organic matter in the dolomitic Middle Jurassic Beddiane sequence hosting the Beddiane lead–zinc deposit. Organic matter occurs in the lower dolostone units of the formation where zinc sulfide mineralization prevails. The upper units, where lead sulfide mineralization is dominant, contain lesser amounts of organic matter. The organic matter in the Beddiane sequence consists of macerals, amorphous kerogen, and solid bitumen, inertinite and vitrinite are ubiquitous. The amount of exinite increases toward mineralized areas but the ratio exinite/kerogen remains constant. Two types of vitrinite are considered on the basis of their reflectance: Vt1 with low reflectance values (0.3–0.5%) and Vt2 with higher values (0.7–1.25%). The ratio Vt1/Vt2 increases and the reflectance values for Vt1 decrease toward the zinc-prevailing units, Organic matter associated with the mineralization exhibits features such as oxidation halos and desiccation cracks, together with a low-fluorescent exinite. The association of the kerogen content, the trend in reflectance values, and the alteration features of the Mississippi Valley-type Beddiane deposit support the hypothesis that the regional flow of hot brines associated with the mineralization process was the cause of anomalous heating, that the occurrence of exinite maceral and its associated gas played a role in the ore deposition, and that the new chemical equilibrium reached by the zinc-dominant host rock after ore deposition is responsible for the suppressed reflectance values within and near the ore deposits.

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An isotopic and trace element investigation of gossans from Troodos ophiolite, Cyprus

10.5194/egusphere-egu2020-7018 ◽

2020 ◽

Author(s):

Nina Zaronikola ◽

Vinciane Debaille ◽

Sophie Decree ◽

Ryan Mathur ◽

Christodoulos Hadjigeorgiou ◽

...

Keyword(s):

Massive Sulfide ◽

Major And Trace Elements ◽

Ore Deposits ◽

Point Of View ◽

Economic Point ◽

Troodos Ophiolite ◽

Zinc Isotopes ◽

Copper And Zinc ◽

Vms Deposits ◽

Set Up

The Troodos ophiolite is widely accepted to be a fragment of Mesozoic oceanic crust, which uplifted during Alpine orogeny, due to the collision of Eurasia and Africa (Gass and Masson-Smith, 1963; Vibetti, 1993; Adamides, 2011; Antivachis, 2015). It belongs to supra-subduction ophiolites, which probably set up during subduction initiation associated with back-arc spreading (Pearce, 1975; Rautenschlein et al., 1985; Pearce and Robinson, 2010; Martin et al., 2019). The Troodos ophiolite is mentioned to be one of the most well studied and well-preserved ophiolitic sequences (Moores and Vine, 1971; Benn and Laurent, 1987; Patten et al., 2017), presenting significant Cyprus-type sulphide deposits (Constantinou and Govett, 1973; Adamides, 2014).Cyprus-type deposits are generally, considered as mafic type volcanogenic massive sulfide deposits (VMS), mainly rich in copper and subsidiary zinc, with average grade of 1.3 &#177; 1.1% Cu and 0.8 &#177; 0.4% Zn (Hannington et al., 1998; Barie and Hannington, 1999; Patten et al., 2016). VMS deposits are formed in the sea floor, along mid-ocean ridges, by the circulation of high temperature hydrothermal fluids, which their source is seawater (Gillis and Robinson, 1988; Richards et al., 1989; Patten et al., 2017; Martin et al., 2019). In many different regions along the Troodos ophiolite, the VMS deposits are covered by thick, Fe oxides enriched gossans (Bear, 1960; Herzig et al., 1991). In general, those can be formed, when the VMS deposits are exposed to weathering and oxidizing conditions (Herzig et al., 1991), but still the conditions for their formation are debated. The studied gossans from Troodos ophiolite are variegated due to the presence of white silica, red hematite and yellow jarosite. Gossans are always a very interesting part of the ophiolitic sequence from an economic point of view, as they present not only significant amount of extractible copper and zinc, but also, gold and silver (Bear, 1960; Herzig et al., 1991).We aim to examine the major and trace elements of gossans, which have been collected from different mines (West Apliki, Skouriotissa and Agrokipia mines) of Troodos ophiolite, and define their enrichment or depletion in copper and zinc, by coupling copper and zinc stable non-traditional isotopes. We combined copper with zinc isotopes in a very novel and original approach in order to give information about the conditions prevailing in the system of interest. As many authors mentioned before, supergene enriched environments are the best places to examine the behavior of Cu isotope fractionation under the weathering conditions of ore deposits (Mathur et al., 2008). On the other hand, Zn isotopes are not redox sensitive, but pH-sensitive (Pons, 2016). By coupling them, it can bring light in understanding the way, the nature of fluids that led to gossans formation and their enrichment in copper and zinc in different locations of Troodos ophiolite.

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Symposium: Role of organisms and organic matter in ore deposition/Le rôle des organismes et de la matière organique dans la formation des gisements métallifères

Canadian Journal of Earth Sciences ◽

10.1139/e85-203 ◽

1985 ◽

Vol 22 (12) ◽

pp. 1890-1892 ◽

Cited By ~ 2

Author(s):

R. W. Macqueen

Keyword(s):

Organic Matter ◽

Ore Deposits ◽

Sulphate Reduction ◽

Sulphide Mineral ◽

Special Session ◽

Geochemical Cycle ◽

Lead Zinc ◽

Pine Point ◽

Earth’S System ◽

Ore Deposition

The following seven papers were presented on May 16, 1984, at the Geological Association of Canada and Mineralogical Association of Canada joint annual meeting. The special session, organized by R. W. Macqueen and J. A. Coope, contained 10 papers and was sponsored by the Mineral Deposits Division of the Geological Association of Canada.Our objective in organizing the special session was to examine organically based processes and relationships that may be of major importance to the origin of ore deposits. As noted by Fyfe (1984), the concept of the geochemical cycle focuses attention on pathways of chemical elements and isotopes of the Earth's system during geologic history. It is clear from the chemistry of carbon-rich materials that a wide range of elements is concentrated directly or indirectly by biological processes operating as part of the geochemical cycle. Two of the papers of the special session examine some of these concentration processes, although definitive links to actual ore deposits cannot be made yet. Beveridge and Fyfe document the remarkable ability of the anionic cell walls of certain bacteria to concentrate metals and to provide sites for nucleation and growth of minerals. In a related paper, Mann and Fyfe show that several species of simple freshwater green algae readily concentrate large amounts of uranium under both experimental and natural conditions (Elliot Lake and Thames River, Ontario).Two papers deal with aspects of sulphate reduction. Birnbaum and Wireman describe controlled experiments that suggest that sulphate-reducing bacteria may be involved in the selective replacement of sulphate-evaporite minerals by silica and in the precipitation of silica in association with sulphide mineral phases in banded iron formations. Their work focuses directly on the effect that bacterial sulphate reduction has on silica solubility. Trudinger et al. examine the question of mechanisms of sulphate reduction at temperatures less than 200 °C and the bearing this has on origin of sulphide for low-temperature sulphide ore deposits. Although there is empirical evidence favouring abiological sulphate reduction at temperatures in the vicinity of 100 °C, Trudinger et al. have not been able to demonstrate abiological reduction of sulphate under controlled laboratory conditions and at temperatures under about 200 °C. Perhaps catalysts, as yet undiscovered, are involved in this process in nature.Impressive progress has been made in understanding the diagenetic evolution of organic matter in response to heat and pressure in geological environments: excellent reviews are found in Barnes et al. (1984) and Bustin et al. (1985). Simoneit's paper examines and reviews the genesis of petroleum in a most unusual setting, that of the active ocean ridge spreading centre of Guaymas Basin, Gulf of California. There, in the vicinity of black smokers and associated metallic sulphide deposits, petroleum originates instantaneously geologically as a result of hydrothermal activity. The question of genetic involvement of organic matter in the origin of the metallic sulphides (e.g., reduction of sulphate to H2S) cannot be answered yet for this setting with the available data.The final two special session papers included here are concerned with organic matter associated with mineralization in Canadian Shield Precambrian settings. Willingham et al. demonstrate that Elliot Lake – Blind River Early Proterozoic uranium deposits with minor amounts of associated gold also contain kerogen-like organic matter. Some of this organic matter has anomalously rich amounts of gold and uranium and appears to have originated as mats of cyanobacteria, possibly with the ability to concentrate these metals. For a number of settings in the Archean-aged Abitibi greenstone belt of Ontario and Quebec, Springer demonstrates that carbon, at least partly of organic origin, is closely associated with some gold deposits. Her interpretation is that carbon activated by shear-zone-associated hydrothermal fluids has provided sites for fixing some of the gold.Three of the papers given at the special session are not included here. H. T. Shacklette reviewed metal uptake by young conifer trees, demonstrating that nursery-grown seedlings of several species readily concentrated a variety of metals, including lead, zinc, tin, and gold, over a 7 year period. This work is of interest to those involved in geochemical prospecting and is now published elsewhere (King et al. 1984). R. W. Macqueen presented quantitative data on the genesis of sulphide by abiological bitumen–sulphate reactions at the Pine Point lead–zinc property, Northwest Territories, Canada (Macqueen and Powell 1983; Powell and Macqueen 1984). Although Trudinger et al. have not been able to demonstrate abiological reduction of sulphate at temperatures approximating those of Pine Point [Formula: see text], the data presented by Macqueen (Powell and Macqueen 1984) are consistent with the amounts, alteration, and composition of bitumens at Pine Point, as well as with the presence of native sulphur and the sulphur isotope compositions of the various Pine Point sulphur species. This work is continuing, and a more extensive account is in preparation. J. R. Watterson examined relationships between freezing climates and the local chemical behaviour of gold in the weathering cycle, concluding that ice-induced accumulation of organic acids, bacteria, and other organic matter at mineral surfaces may increase rates of chemical attack, leading to dissolution of normally insoluble metals such as gold (Watterson 1986).Interest in organic aspects of the geochemical cycle, including ore deposition, is growing dramatically (e.g., Fyfe 1984). Although the following papers address a limited range of topics within the field, they do indicate some of the diversity and variety of active processes and associations between metallic elements and organic components. Perhaps, in the not too distant future, we will be able to identify or even discover whole classes of ore deposits that owe their origin directly to organic influences operating within the geochemical cycle.

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