Abstract:

The Lunshan gold deposit is a newly discovered small gold deposit in Jiangsu Province. The gold bodies are hosted in the Cretaceous Yangchong Formation, including carbonaceous mudstone and argillaceous siltstone.The metal minerals are mainly composed of pyrite with minor chalcopyrite, galena and sphalerite.Whereas quartz, calcite, fluorite and sericite are the main non-metallic minerals.Metallogenic stages include sedimentary diagenetic stage, hydrothermal stageⅠand hydrothermal stageⅡ. The sedimentary diagenetic stage and hydrothermal stageⅠare the main metallogenic stages.An integration of optical microscopy, scanning electron microscopy equipped with energy dispersive system and electron microprobe was used to study the occurence, distribution and enrichment mechanism of gold in the Lunshan gold deposit.The results indicate that gold occur as microscopic invisible and native species.The microscopic invisible gold is present as nanopa-rticles of native gold (Au⁰) and solid solution gold (Au⁺) in pyrite.The visible native gold occurs either as intergranular gold between detrital quartz grains or as fissure gold in the detrital quartzs.The Co/Ni ratios of framboidal, fine-grained and acicular pyrites are greater than one, indicating that they were affected by the late hydrothermal fluids.The preliminary gold enrichment in the sedimentary diagenetic stage superimposed by later ore-forming fluids lead to the formation of the Lunshan gold deposit.

Key words: Lunshan gold deposit, metallogenic stage, occurrence, enrichment , mechanism, Jiangsu