Hydrogen Isotopic Composition of Groundwater at the Kaskadnoye Gold Ore Deposit (Kuznetsk Alatau)
Abstract Generated abstract
This study examines variations in the hydrogen isotopic composition of groundwater with depth at the Kaskad gold ore deposit in the Kuznetsk Alatau. Water samples from mine adits down to 650 m were analyzed for deuterium by the flotation method and compared with chemical composition and hydrogeological conditions. The authors interpret the waters as predominantly of infiltration origin within an intensively flushed fractured structure, but find that deuterium content generally increases with depth, reaching the highest value in the deepest sampled water, where chemical data indicate impeded water exchange and some metamorphization. Deviations from the depth trend are attributed plausibly to fracture-controlled circulation and seasonal differences in recharge by snowmelt and rainwater.
Full Text
HYDROGEN ISOTOPE COMPOSITION OF GROUNDWATER OF THE KASKAD GOLD-ORE DEPOSIT
(KUZNETSK ALATAU)
V. G. Ivanov, A. P. Gribanov, T. M. Slezova
(Presented by Professor P. A. Udodov)
The change in the isotopic composition of groundwater with depth is most conveniently traced in underground mine workings. For this purpose, the authors collected water samples in the adits of the Kaskad deposit (Saralinskoe ore field, Kuznetsk Alatau). The deepest adit (14th level) is located at a depth of 650 m from the surface.
The deuterium content in the groundwater was determined by the flotation method, with normalization of the isotopic composition of the water by oxygen (Brodsky 1957, Shatenshtein 1957).
The groundwater of the Kaskad deposit area, within the interval studied (down to 650 m), is of infiltration origin. This is due to a number of physiographic and structural factors:
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The confinement of the area to the axial part of the Kuznetsk Alatau and, consequently, its maximum uplift (absolute elevations 1200–1600 m), a high degree of dissection of the relief (relative elevations 300–900 m), and increased humidity (700–900 mm per year).
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The accumulation in winter, on slopes of eastern exposure, in stream valleys, and in cirque basins, of large masses of snow, which serve as an additional source of recharge by meltwater during the summer period.
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The widespread development of Quaternary deposits, in most cases highly permeable and forming aquifer horizons.
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The presence of regional fracturing of rocks and numerous zones of disjunctive disturbances, which serve as pathways for the circulation of groundwater.
According to the classification of N. K. Ignatovich (1950), the area studied belongs to the zone of intensive water exchange, to an open, flowing, well-flushed structure.
The water-bearing rocks are effusive-sedimentary formations (acidic and basic effusives, their tuffs, conglomerates, sandstones, clayey, carbonaceous, carbonaceous-clayey, siliceous, clayey-siliceous, carbonaceous-siliceous, and carbonate-clayey shales), with rare lenses of limestones and marls, intruded by small intrusions of dioritic, gabbro-dioritic, and plagiogranitic composition. The questions of the age of the rocks (Precambrian or Cambrian) and some questions of the structure of the area have not been definitively resolved (Bazhenov 1961).
The deuterium content in the waters studied (Table 1) is, for the most part, lower than in the standard water (we adopted as the standard—
water of the Tom River). The waters of the upper zone are the most depleted in deuterium (\(-1.6\gamma\)). With depth, the deuterium content increases (with the exception of samples 5c and 6c).
The waters (sample 12c), taken, as far as possible, from the greatest depth (650 m), are characterized by the highest deuterium content (\(+1.3\gamma\)).
With depth there is a slowing of groundwater circulation. In the present case, at a depth of 650 m, close to the local base level of erosion, the rate of circulation is rather insignificant (a zone of impeded water exchange). In chemical composition these waters differ markedly from the waters of the upper zone. Thus, the latter are characterized by a hydrocarbonate–sulfate–calcium–magnesium or magnesium–calcium composition. The waters of the zone of impeded water exchange are characterized by a hydrocarbonate–sodium composition, with no sulfate ion and with an elevated chloride-ion content (11.1 mg/l). The absence of sulfate ion, together with other indicators, points to a reducing environment. Thus, the chemical composition of the deep waters indicates a certain degree of their metamorphization, in the course of which enrichment in deuterium apparently occurred.
Enrichment of waters in heavy isotopes at depth, according to E. V. Pinneker (1966), occurs as a result of subsurface evaporation, the presence of elevated temperatures, sorption of light isotopes by rocks, dehydration of certain minerals, etc.
An increase in deuterium content in groundwater with depth is also indicated by F. A. Alekseev and V. V. Kontsova (1964), A. E. Babinets (1961), and other investigators. Exceptions to the general regular increase in deuterium content with depth are samples 5c and 6c, in which its content is lower in comparison with waters situated at lesser depth. The waters opened by borehole 5c are also characterized by low total mineralization and a hydrocarbonate–calcium composition, in contrast to the hydrocarbonate–magnesium composition of the overlying waters.
An analogous phenomenon in the same area at the Vstrechnoye deposit was noted by V. M. Matusevich (1964), where, likewise, on deeper horizons, owing to the presence of strongly filtering fractures, a peculiar inversion is observed, expressed in a sharp decrease in total mineralization and in the sum of microcomponents.
A decrease in deuterium content as a result of isotopic exchange with hydrogen sulfide (Grinberg and Petrikovskaya, 1965) and organic matter (Babinets, 1961) is unlikely in the present case, since hydrogen sulfide and hydrocarbons were not detected in the waters.
It should be taken into account that infiltrating atmospheric precipitation in different seasons of the year may be characterized by different deuterium contents. Thus, in the spring–summer period, significant masses of snowfield meltwater depleted in deuterium infiltrate. In the autumn period, when the snowfields have already melted, groundwater recharge occurs through rainwater, which is usually less depleted in deuterium than snow waters (especially autumn rains). Therefore, in the autumn period, waters with a higher deuterium content enter the upper zone than the spring–summer waters that infiltrated earlier and, consequently, penetrated to a greater depth.
Further studies of the isotopic composition of groundwater and atmospheric precipitation in this area will make it possible to solve a number of theoretical questions connected with the formation of groundwater and to outline criteria for the practical use of data on their isotopic composition.
Chemical and isotopic composition of groundwater from the Kaskadnaya adit
Table 1
| No. | Point no. | Sampling location | Aquifer character | Depth, m | pH | CO2, mg/L | H2SiO3, mg/L | NO2, mg/L | NO3, mg/L | SO4, mg/L | Cl, mg/L | HCO3, mg/L | Ca, mg/L | Mg, mg/L | Na, mg/L | NH4, mg/L | Fe, mg/L | Fe, mg/L | Total mineralization, mg/L | Salt-composition formula | Cu | Zn | Ag | Ni | Co | Mo | Sr | Ti | Mn | Ba | P |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | 8c | 4th horizon | capillary | 34 | -1.5 | 3.7 | 5.2 | — | — | 60 | 4.7 | 280 | 30 | 38.8 | 6.9 | 0.2 | — | — | 424 | HCO3_{13}SO4_{36}Cl2 Mg_{66}Ca_{30}Na5 |
0.23 | 0.69 | 0.23 | — | — | — | — | 0.23 | 6.9 | — | — |
| 2 | 1c | horizon | capillary | 43 | -1.3 | 3.7 | 11.05 | 0.3 | — | 53 | 4.7 | 256 | 35 | 36.4 | 13.7 | 0.2 | — | — | 399 | HCO3_{66}SO4_{26}Cl1 Mg_{58}Ca_{30}Na12 |
0.7 | 2.2 | — | 22 | 0.7 | trace | — | — | trace | — | — |
| 3 | 3c | 5th horizon | capillary | 53 | -0.3 | 3.7 | 10.6 | — | — | 30 | 4.7 | 268.4 | 30 | 37.7 | 11.5 | 0.1 | — | — | 382 | HCO3_{68}SO4_{8}Cl2 Mg_{55}Ca_{29}Na14 |
<0.9 | — | — | 45 | — | — | — | — | 27 | — | — |
| 4 | 7c | 6th horizon | " | 54 | +0.3 | 3.7 | 5.9 | — | — | 60 | 4.7 | 329.5 | 35 | 44.9 | 45.9 | 0.1 | — | — | 420 | Mg_{40}Ca_{30}Na_{30} HCO3_{80}SO4_{18}Cl2 |
0.7 | 13.6 | — | 0.68 | — | — | — | — | trace | — | — |
| 5 | 4c | 7th horizon | well, footwall | 113 | -0.3 | 3.7 | — | — | — | 75 | 4.7 | 378.2 | 35 | 59.5 | 27.5 | 0.3 | — | — | 580 | Mg_{55}Ca_{25}Na_{19} HCO3_{66}SO4_{30}Cl1 |
0.65 | — | — | 0.65 | — | — | — | — | 4.3 | — | — |
| 6 | 6c | 9th horizon | well, footwall | 131 | -0.6 | 3.7 | 10.5 | — | — | 70 | 4.7 | 378.2 | 30 | 59.5 | 32.1 | 0.1 | — | — | 574 | Mg_{48}Ca_{28}Na_{15} HCO3_{53}SO4_{19}Cl1 |
0.7 | 5.1 | — | trace | — | — | — | 0.73 | 7.3 | — | — |
| 7 | 5c | " | well, hanging wall | 153 | 1.3 | 3.7 | 13.0 | — | — | 50 | 4.7 | 158.6 | 25 | 17.0 | 22.9 | 0.1 | — | — | 280 | Mg_{34}Ca_{30}Na_{35} HCO3_{48}SO4_{35}Cl3 |
1.8 | 4.3 | — | 0.61 | — | — | 37 | 0.6 | 37 | trace | 370 |
| 8 | 12c | 14th horizon | well, footwall | 650 | +1.3 | 3.7 | — | 0.01 | — | — | 11.1 | 292 | 10 | 3.65 | 101.1 | 0.2 | — | — | 419 | Ca_{34}Mg_{30}Na_{27} HCO3_{20}Cl5 Na_{25}Ca_{10}Mg5 |
0.4 | — | — | — | — | — | — | 0.42 | 8.4 | — | — |
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