The Role of the Lithological Factor in the Distribution of Gold Ore Occurrences in the Central Part of the Lena Province
Abstract Generated abstract
This paper examines how lithology influences the distribution of gold ore occurrences in the central Lena Province. Using statistical processing of assay data from rocks without visible hydrothermal alteration, it compares gold occurrence across terrigenous, terrigenous-carbonate, and carbonate rock types and relates these patterns to quartz-vein fields and veinlet-disseminated sulfide mineralization. The study finds that gold is present in all examined rock types but is most frequent and enriched in carbonaceous shale and related siliceous complexes, while limestones show lower occurrence. It argues that both quartz-vein and sulfide gold occurrences are concentrated in specific lithological-stratigraphic complexes with elevated carbonaceous matter and primary-sedimentary gold, a relationship important for prospecting and metallogenic mapping.
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THE ROLE OF THE LITHOLOGICAL FACTOR IN THE DISTRIBUTION OF GOLD-ORE OCCURRENCES IN THE CENTRAL PART OF THE LENA PROVINCE
V. V. Kotkin (ISU)
Primary sedimentary rocks of three types, metamorphosed to varying degrees, participate in the geological structure of the central part of the Lena Province:
- Terrigenous rocks (quartz, mica–quartz, carbonaceous–quartz, feldspar–quartz, polymictic, and volcanomictic).
- Terrigenous–carbonate rocks (clastic limestones, calcareous sandstones, siltstones, and shales).
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Carbonate rocks (chemogenic limestones and dolomites). The following combinations of lithological varieties are most typical:
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Predominantly sandstone complexes with subordinate interbeds of siltstones and shales in terms of thickness.
- Predominantly carbonaceous–argillaceous shale complexes with sandstones subordinate in thickness.
- Complexes of rhythmically interbedded oligomictic sandstones, siltstones, and shales, densely saturated with syngenetic iron–magnesian carbonates and pyrite.
- Complexes of interbedded carbonaceous carbonate and terrigenous rocks.
- Carbonate complexes.
Statistical processing of the results of assay analyses of rocks from sections lacking traces of hydrothermal alteration shows the presence of gold in all rock types (Table 1).
Table 1
| No. | Rock name | Number of samples counted | Number of samples with gold, pcs. | Number of samples with gold, % |
|---|---|---|---|---|
| 1 | Shales and siltstones | 458 | 250 | 50 |
| 2 | Sandstones of all types | 454 | 220 | 48 |
| 3 | Limestones | 204 | 67 | 33 |
| 4 | Quartz veins | 1391 | 585 | 42 |
In shale and feldspathic complexes (types 2 and 3), the largest number of samples with gold is observed (up to 70%), while in limestones it is the smallest.
In carbonaceous phyllites the maximum gold contents are observed (tenths of a gram, more rarely 1–2 grams per ton); in the other varieties, hundredths and thousandths of a gram.
Gold in carbonaceous phyllites is of small size and, in its characteristics and features of distribution, is entirely comparable with the primary-sedimentary (chemogenic) gold of Mangyshlak (Nifontov, 1960).
The disseminated primary-sedimentary gold content of the rocks of the Lena district largely determines, along with other factors, the distribution of gold-ore occurrences of the localized type:
1) low-sulfide quartz veins;
2) zones of veinlet-disseminated sulfide mineralization.
Quartz-vein fields, concentrated as zones in the axial parts of anticlinal folds, are confined to definite lithological complexes. Of 71 vein fields of the Bodaibo synclinorium, 48 are located in dark-colored oligomictic complexes of interbedded sandstones, siltstones, and shales; 18—in predominantly shale complexes; and 4—in predominantly sandstone complexes.
The mineralogical composition of the veins reflects the composition of the enclosing rocks. In quartz rocks, monomineralic quartz veins are widespread; in polymictic rocks, feldspar-quartz veins; and in carbonate rocks, calcite-quartz veins.
The gold content of quartz veins is determined by the gold content of the enclosing rocks. As the gold content in the enclosing rocks increases, the gold content in the quartz veins also increases.
The distribution of sulfide gold-ore occurrences of the veinlet-disseminated type has a distinct lithological-structural control.
All known gold-ore occurrences of this type are localized only in carbonaceous silty-pelitic rocks of siliceous composition. Elevated concentrations of gold are controlled by structural factors. The gold content is not high, but it is uniform.
Quartz-vein and sulfide gold-ore occurrences are confined to definite lithological-stratigraphic complexes of siliceous composition with an elevated content of carbonaceous matter and primary-sedimentary gold content.
The influence of the lithological factor on the distribution of gold-ore occurrences in the Lena district must be taken into account when directing prospecting work and when compiling metallogenic and prognostic maps.