Native gold of pseudo-ore habit in the Cretaceous conglomerates (Aldan-Stanovoy shield, south-east of the Siberian Platform)

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Abstract

For the first time, poorly-rounded gold of ore habit was found in intergrowth with quartz, feldspar, ilmenite, zircon and other minerals, along with well-rounded placer gold, when studying the mineralogical and geochemical features of native gold from the Cretaceous conglomerates of the central part of the Aldan-Stanovoy shield. However, upon detailed study, it was found that gold of ore habit belongs to gold of the pseudo-ore habit. This gold is characterized by a pitted-tubercular surface, “intergrowths” of gold with minerals of the host deposits and through holes. Discovery of gold of the pseudo-ore habit in the Cretaceous conglomerates indicates the transformation of placer gold as a result of diagenesis processes, and not the superimposed later ore mineralization. Gold of the pseudo-ore habit was previously discovered in the Devonian conglomerates of the Timan Ridge, as well as in the Jurassic and Permian conglomerates of the east of the Siberian Platform. Presence of such gold was the reason for searching for ore sources in the studied territories, which did not lead to positive results. In general, identification of gold of pseudo-ore habit in conglomerates of various ages from the Archean to the Cenozoic makes it possible to more correctly predict the formation of gold deposits and select search methods.

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About the authors

Z. S. Nikiforova

Diamond and Precious Metal Geology Institute, Siberian Branch, Russian Academy of Sciences

Author for correspondence.
Email: znikiforova@yandex.ru
Russian Federation, Yakutsk

A. I. Zhuravlev

Diamond and Precious Metal Geology Institute, Siberian Branch, Russian Academy of Sciences

Email: znikiforova@yandex.ru
Russian Federation, Yakutsk

Е. Е. Loskutov

Diamond and Precious Metal Geology Institute, Siberian Branch, Russian Academy of Sciences

Email: znikiforova@yandex.ru
Russian Federation, Yakutsk

A. I. Ivanov

Diamond and Precious Metal Geology Institute, Siberian Branch, Russian Academy of Sciences

Email: znikiforova@yandex.ru
Russian Federation, Yakutsk

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2. Fig. 1. Map-scheme of the location of the studied objects. 1 - Cenozoic deposits; 2 - Mesozoic volcanic formations; 3 - Mesozoic terrigenous-sedimentary rocks making up the depressions (Nv - Nevacha); 4 - Mesozoic alkaline massifs; 5 - Proterozoic granites; 6 - Proterozoic basic rocks; 7 - stratified metamorphic complexes of the Stanovaya region (St) (Proterozoic); 8 - Archean ultrabasic rocks; 9 - stratified metamorphic complexes of the South Aldan region (Archean) (Tn - Tangrak block, Zv - Zverevsky block); 10 - faults; 11 - diaphthorites; 12 - placer area of ​​the Yursky stream.

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3. Fig. 2. Morphology of gold (a) and granulometric composition of native gold (b) from conglomerates, values ​​in %. Forms of gold (a): 1 – lumpy, 2 – interstitial, 3 – lamellar. Gold size (b), mm: 4 – <0.25; 5–0.25–0.5; 6–0.5–1; 7 – >1.

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4. Fig. 3. Morphological forms of gold and their surface: a, b, c – well-rounded flakes; surface: a – shagreen, b – shagreen with a break in the edge of the gold grain; c – coarsely pitted with a through hole and with imprints of indented minerals; g, d, e – lamellar with a coarsely shagreen surface, on which indented minerals are observed. Scale bar 0.1 mm.

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5. Fig. 4. A section of gold showing loose intergrowth of gold (Au) with zircon (Zrn). Scale bar 0.05 mm.

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6. Fig. 5. Pseudo-ore gold in Devonian conglomerates of the Timan Ridge. Qz – quartz, ilm – ilmenite. Scale bar 0.1 mm.

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7. Fig. 6. a, b – surface of gold grains with imprints of minerals pressed into them, obtained as a result of the experiment; c – surface of gold from chalk conglomerates, on which pressed quartz (Qz) and a through hole are also observed. Scale bar 0.1 mm.

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8. Fig. 7. Fineness of well-rolled and poorly-rolled forms and aggregates of gold.

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