Hydrothermal-sedimentary dolomite — a case from the Middle Permian in eastern Junggar Basin, China

Abstract

The Middle Permian Lucaogou Formation in the Jimusar Sag, eastern Junggar Basin, NW China, was deposited in a salt lake within an intracontinental rift basin with intense hydrothermal activity. Hydrothermal-sedimentary dolomite in the form of three types of dolostones, namely, analcime-feldspar dolostone (AFD), silicic dolostone (SD) and buddingtonite-albite dolostone (BAD), related to syn-sedimentary hydrothermal activity at lake bottom was discovered. The characteristics and formation mechanism of the dolomite were studied based on micron-scale petrographic and isotopic geochemical research. The syn-depositional formation of these dolostones was indicated by their rock-mineral features and syn-sedimentary deformation stage. The dolomite was composed of relatively poorly ordered proto-dolomite crystals with micron-sized spherical or sub-spherical morphology and coexisted with hydrothermal minerals, including analcime, buddingtonite, albite and chalcedony. Albite clasts were replaced by the dolomite, indicating high-temperature conditions during formation. The remarkably low strontium isotopic compositions of the dolostones (87 Sr/ 86 Sr with an average of 0.705687) indicated that mantle-derived materials might have involved in the ore-forming fluid. The dolostones had positive δ 13 C PDB values (with an average of 6.94‰) and negative δ 18 O PDB values (with an average of − 8.12‰). Based on the δ 18 O PDB values, the formation temperatures of the dolomite were at least~25°C higher than those of the penecontemporaneous dolomite in the Lucaogou Formation in the study area. It is concluded that the dolomite precipitated from hydrothermal fluid erupting at the lake bottom. The possible genetic models are described. We suggest that the hydrothermalsedimentary dolomite is an important genetic type, and this study may help increase the awareness of this understudied type of dolomite.

Assessment of the interval heat flow and thermal resistance at the Faltu-1 well, Borno basin, NE Nigeria

“…Similarly, when intrusions interact with hydrothermal fluids carrying high metal concentrations outward, skarn deposits are formed by the replacements of limestone, calcareous rocks, or dolomite to produce a variety of minerals including oxide minerals such as magnetite, sulfide minerals such as chalcopyrite, silicate minerals such as epidote, or the tungstate minerals scheelite. Associated with skarn deposits, which can be either massive and discordant, or stratiform and concordant, are such elements as tungsten, copper, molybdenum, iron, gold, tin, lead, zinc and silver (Bevins, 1994;Jamtveit et al 2004;Richter et al 2018;Zhang et al 2020). Economics permitting, zones in the vicinity of magmatic intrusions may be mined for any occurring mineral when the oil is eventually exhausted or when the hole is dry.…”

Lacustrine dolomite in deep time: What really matters in early dolomite formation and accumulation?

“…Dolomites of the two types of alkaline brackish lakes have similar carbon and oxygen isotopic compositions, suggesting that their dolomites were genetically related. 13 C values of dolomite from alkaline brackish lakes are positive, ranging from 0 to +10‰ (V-PDB), while their δ 18 O values are mostly negative, ranging from − 20 to 0‰ (V-PDB) Wen et al, 2013;Wang et al, 2014a;Song et al, 2015;Qu et al, 2017;Wei et al, 2017;Zhang et al, 2020;Yang et al, 2020;Wu et al, 2022) (Fig. 8) (Table 2).…”

“…The first model highlights the fundamental controls of hydrothermal activity on lake water hydrochemistry and temperatures and suggests that the laminated dolomites of alkaline brackish lakes are hightemperature (>60 • C) primary precipitates (Wen et al, 2013;Song et al, 2015;Yang et al, 2020Yang et al, , 2021aZhang et al, 2020;Jiao et al, 2023). In this model, hydrothermal fluids could locally supply abundant Mg 2+ from a deep source into lakes and increase water temperatures, creating favorable physico-chemical (e.g., pH, Mg/Ca) conditions for primary dolomite precipitation.…”

“…5D-F), whereas calcite crystals of similar size are very rare (Guo et al, 2021), suggesting the possibility of primary dolomite. Besides dolomite, there are clays, natrolite [Na 2 Al 2-Si 3 O 10 ⋅2H 2 O], analcime, quartz, K-feldspar and albite in dolomitic tuffites and tuffaceous dolomites Liu et al, 2012;Zhang et al, 2020). Among the various ancient lacustrine dolomites of China, dolomitic tuffites and tuffaceous dolomites contain largest dolomite crystals in matrix and aggregates, generally ranging from 15 to 70 μm (Fig.…”

“…Hydrothermally influenced primary dolomite formation model can explain the genesis of laminated dolomudstones, analcimic dolomites, albitic dolomites, and/or dolomitic analcimolites in alkaline brackish lakes (Liu et al, 2012;Wen et al, 2013;Yang et al, 2020Yang et al, , 2021aZhang et al, 2020;Jiao et al, 2023) within rift basins. The presence of primary lamination (Fig.…”