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Saqisan |
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Guangxi, China |
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U
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The Saqisan uranium deposit is located in Daxin County, ~160 km west of Nanning in Guangxi Province, southern China, just north of the Vietnamese border, and was the largest known breccia-hosted uranium deposit in China in 2002 (#Location: 22° 54' 29"N, 106° 40' 59"E).
The oldest rocks exposed in this part of China are metamorphosed Cambrian sandstone, which is unconformably overlain by weakly metamorphosed Ordovician sandstone and shale. Unmetamorphosed Devonian carbonate with a total thickness >700 m unconformably overlies the Ordovician sandstone and is conformably followed by unmetamorphosed Carboniferous carbonate. The Saqisan deposit is hosted by carbonaceous pelitic limestone, dolomitic limestone of the middle Devonian whilst the Sanbaqi Deposit is within similar Lower Carboniferous rocks (Min and Wu, 1998).
The orebodies are located in solution-collapse breccias along faults and unconformities between different strata, and within cores of anticline or syncline, in which faulting and karsting have been developed. The matrix of the breccia is composed of carbonaceous clays with silt to pebble-sized limestone fragments. The uranium mineralisation occurs in the dark grey matrix of the dark-grey limestone solution-collapse breccia and interconnected palaeokarst passages and caverns that were filled with consolidated, mineralised, clastic sedimentary rocks which constitute the bulk of the orebodies. The orebodies have a variable morphology, including lenticular, hopper-shaped, nested, prismatic and irregular bodies. Wall-rock alteration is generally weak and includes assemblages of silica, chlorite, dolomite, pyrite and carbonate. The dominant gange and ore minerals are carbonates (calcite and dolomite), pitchblende, coffinite, pyrite
and marcasite, accompanied by minor pentlandite, millerite, ullmannite, molybdenite, niccolite, sphalerite, galena, chalcopyrite, antimonselite and quartz. Pitchblende, as the dominant primary uranium mineral, occurring as veinlets ranging from 0.1 to 5 mm in thickness and disseminated of 0.01 to 0.5 mm grains.
A minor amount of uranium was adsorbed onto breccia clays and organic matter in the matrix. At the Saqisan Deposit, there is no macroscopically visible primary uranium mineral in the ore (Min and Wu, 1998).
Two stages of primary uranium mineralisation are recognised, namely (after Min et al., 2002):
i). The early stage (I) mineralisation is the most important for uranium as it accounts for 60% of Saqisan's total uranium tonnage. Stage I mineralisation formed low-grade ore. The uranium in stage I ores predominantly occurs as very fine pitchblende in the clay-rich breccia matrix. Isotopic data indicate that biogenic pyrite in the host carbonate may have been the major source of sulphur in the mineralising fluids and that most of the precipated CO2 and HCO3- during stage I mineralisation was derived from bicarbonate dissolved out of the marine host carbonate.
ii). The late stage (II) mineralisation, which accounts for the remaining 40% of Saqisan's total uranium tonnage, is hosted by strongly silicified, foliated, and mylonitised host limestones. The uranium in stage II ores mainly occurs as pitchblende veinlets, 0.1 to 2 mm wide, and as disseminated pitchblende grains ranging from less than 0.1 to 1 mm in size. It is postulated that the high-grade uranium ore of stage II is the product of multiple, superimposed reconcentration of uranium from the stage I ore by low- to moderate-temperature (110 to 251°C) uranium-enriched hydrothermal brines driven by a regional heating event, such as the late Yanshanian tectonism.
No published tonnage or grade statistics have been encountered to date.
The most recent source geological information used to prepare this decription was dated: 2002.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
Saqisan
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Selected References:
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Min M Z, Luo X Z, Mao S L, Zheng D Y and Shen B P 2002 - The Saqisan Mine - a paleokarst uranium deposit, South China: in Ore Geology Reviews v19 pp 79-93
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Min, M. and Wu, J., 1998 - Stable isotope studies of paleokarst-hosted uranium deposits in China: in Geochemical Journal v.32, pp. 103-115.
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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