Discovery of galena in Tertiary pebbly coquina and its implication in mineralization |
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| Authors: | Song Tianrui Zhang Liyan |
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| Institution: | (1) Institute of Geology, Chinese Academy of Geological Sciences, Beijing;(2) Beijing Institute of Mining and Metallurgy, China |
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| Abstract: | A suite of terrestrial-marine transitional carbonate beds occur in the Lower Tertiary of the Kuqa Basin, Xinjiang. The pebbly
coquina, Paleocene in age, is distributed along the southern pediment of the Tianshan Mountains north of Baicheng, where Pb-mineralization
has been observed for the first time.
The pebbly coquina consists of well-rounded quartzitic pebbles, quartz sands, shell fossils, shell fragments and equigranular
fecal pellets.
Four types of carbonate minerals have been revealed: 1) euhedral dolomite (Mg60Ca40)CO3, 2) anhedral dolomite (Mg57Ca43)CO3, 3) dolomitic calcite (Mg20Ca80)CO3 and magnesitic dolomite with a trace amount of Pb(Mg73Ca27)CO3.
Five types of galena filling the pebbly coquina have been found: 1) in the shell tower end, 2) on the inner shell wall, 3)
on the outer shell wall, 4) around the shell wall, and 5) among shell fragments. The galena replacement took place mainly
in the early stage of diagenesis. Stable isotope analyses show (δ13C values range from −0.8 to +2.3 and δ18O values from −0.1 to +0.5, indicating a marine environment under the influence of fresh water, which is consistent with the
result of megascopic facies analysis in paleogeography.
It is concluded that the discovery of galena in the Tertiary pebbly coquina in the north of Baicheng, Xinjiang may provide
new clues to the searching for strata-bound Pb-Zn deposits in the vast area of northern Tarim Basin. |
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