Judging the Sedimentary Environment of the Silicalite Formation on the Chemical Characteristics of Rocks in Western Qinling

Liu Jiajun; Liu Jianming; Zheng Minghua; Zhou Yufeng; Gu Xuexiang; Zhang Bin; Lin Li; Zhou Dean

The Cambrian silicalite formation, composed of black chert and black slate, is the host-rock of Laerma and Qiongmo gold deposits in western Qinling.The ore-bearing chert is characterized by bedded, laminated, mas- sive and pseudobrecciated structures which change regularly in space.The thickness of a chert bed generally varies from 30 to 200 meters.Host elements are simple and concentrated in the chert.Besides SiO₂(95.30 % on average), only FeO, Fe₂O₃ and P₂O₅ reach or are more than 1.0 %.The ratios of FeO/Fe₂O₃ in all chert samples are mainly greater than 1, but the ratios of Sr/Ba are less than 1.The organic carbon concentrations of silicalite formation range mostly from 0.12 % to 8.14 %, the highest concentration being 22 %.REEs(rare- earth elements) are characterized by a low total content (ranging between 3.29×10^-6～100×10^-6), nega- tive Ce anormal and a gradually increasing NASC —normalized value with increasing atomic number of REEs. The δ³⁰Si values of the chert in the area range mainly from + 0.4 ‰to 0.8 ‰.All the geochemical characteris- tics of the silicalite formation manifest that the silicalite formation deposited in the deep and half- deep sea en- vironment.

Judging the Sedimentary Environment of the Silicalite Formation on the Chemical Characteristics of Rocks in Western Qinling

1 lnstitute of Geochemistry, Chinese Academy of Sciences, Guiyang, 550002;

2 The Research Center of Mineral Resources Exp loration, CAS, Beijing, 100101;

3 lnstitute of Mineral Deposits, Chengdu University of Technology, Chengdu, 610059;

4 Beijing Research lnstitute of Geology, China National Nuclear Corporation, Beijing 100029

Received Date: 1997-09-04

Rev Recd Date: 1998-03-30

Publish Date: 1998-08-10

Key words:

Abstract: The Cambrian silicalite formation, composed of black chert and black slate, is the host-rock of Laerma and Qiongmo gold deposits in western Qinling.The ore-bearing chert is characterized by bedded, laminated, mas- sive and pseudobrecciated structures which change regularly in space.The thickness of a chert bed generally varies from 30 to 200 meters.Host elements are simple and concentrated in the chert.Besides SiO₂(95.30 % on average), only FeO, Fe₂O₃ and P₂O₅ reach or are more than 1.0 %.The ratios of FeO/Fe₂O₃ in all chert samples are mainly greater than 1, but the ratios of Sr/Ba are less than 1.The organic carbon concentrations of silicalite formation range mostly from 0.12 % to 8.14 %, the highest concentration being 22 %.REEs(rare- earth elements) are characterized by a low total content (ranging between 3.29×10^-6～100×10^-6), nega- tive Ce anormal and a gradually increasing NASC —normalized value with increasing atomic number of REEs. The δ³⁰Si values of the chert in the area range mainly from + 0.4 ‰to 0.8 ‰.All the geochemical characteris- tics of the silicalite formation manifest that the silicalite formation deposited in the deep and half- deep sea en- vironment.

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Judging the Sedimentary Environment of the Silicalite Formation on the Chemical Characteristics of Rocks in Western Qinling

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