Hydrothermal Origin of Top Sinian Chert Formation at Gusui,Western Guangdong,China:Petrologic and Geochemical Evidence

Yongzhang ZHOU; Guangzhi TU; Edward H. CHOWNJayanta GUHA; Huangzhang LU

The Sinian ( Precambrian ) chert formation occurs at Gusui,western Guangdong Province,southern China,and is an integral part of the source strata of the Hetai gold field. The presence of the chert formation offers an excellent opportunity to evaluate the possible hydrothermal system and its role in the formation of the.source strata. The Precambrian chert from Gusui is characterized by bedded, laminated,massive and pseudobrecciated structures, and the depletion of TiO₂,AI₂O₃and most trace elements. However, it is enriched in Ba,As, Sb, Hg and Se,which are considered as diagnostic elements of hydrothermal sediments. In the Al一Fe一Mn ternary diagram,it falls into the“hydrothermal field ". Correspondence analysis and factor analysis reveal that many elements show up in the factor that represents the leaching of country rocks by hydrothermal solution,and is the very characteristic element association of the geochemically anomalous South China basement. REE are characterized by a low total content and a gradually increasing NASC一normalized value with increasing atomic number of REE, ranging between the upper and the lower limits of typical hydrothermal deposits.The petrologic and geochemical evidences suggest a hydrothermal origin for the chert. It may have formed in a Precambrian rift or extension zone developed within the Yunkai marginal geosyncline.with a fault system linkihg to an unknown heat source at depth.

Hydrothermal Origin of Top Sinian Chert Formation at Gusui,Western Guangdong,China:Petrologic and Geochemical Evidence

1 Institute of Geochemistry,Guangzhou Branch, Chinese Academy of Sciences 510640;

Publish Date: 1994-09-10

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Abstract: The Sinian ( Precambrian ) chert formation occurs at Gusui,western Guangdong Province,southern China,and is an integral part of the source strata of the Hetai gold field. The presence of the chert formation offers an excellent opportunity to evaluate the possible hydrothermal system and its role in the formation of the.source strata. The Precambrian chert from Gusui is characterized by bedded, laminated,massive and pseudobrecciated structures, and the depletion of TiO₂,AI₂O₃and most trace elements. However, it is enriched in Ba,As, Sb, Hg and Se,which are considered as diagnostic elements of hydrothermal sediments. In the Al一Fe一Mn ternary diagram,it falls into the“hydrothermal field ". Correspondence analysis and factor analysis reveal that many elements show up in the factor that represents the leaching of country rocks by hydrothermal solution,and is the very characteristic element association of the geochemically anomalous South China basement. REE are characterized by a low total content and a gradually increasing NASC一normalized value with increasing atomic number of REE, ranging between the upper and the lower limits of typical hydrothermal deposits.The petrologic and geochemical evidences suggest a hydrothermal origin for the chert. It may have formed in a Precambrian rift or extension zone developed within the Yunkai marginal geosyncline.with a fault system linkihg to an unknown heat source at depth.

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Hydrothermal Origin of Top Sinian Chert Formation at Gusui,Western Guangdong,China:Petrologic and Geochemical Evidence

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