Geological And Geochemical Characteristics Of Beiya Gold Deposits

Beiya gold deposit is the only super large iron gold polymetallic deposit relatedto Alkali plutonic rock in Jinshajiang Ailaoshan metallogenic belt. On the basis ofprevious researches, through ore microscopy, metallic minerals genetic mineralogy,palynology and X-ray diffraction and scanning electron microscopy and otherresearch, this paper has achieves the following achievements:Magmatism peak period of the Jingshajiang Ailaoshan alkali rich porphyry belt isabout35Ma, with the Cu-Au-Mo deposit in this belt formed at the same time. Beiyagold deposit is a super large gold polymetallic deposit in this belt and its formation isclosely related to the rich alkali porphyry intrusion. The Pb, S, O and C isotopiccharacteristics show that the ore forming fluids were derived mainly from mantle orcrust-mantle mixed layer and other deep source.Through the mineralography and probe data analysis, obtained the chemicalcomposition of chalcopyrite, pyrites and other ore minerals of the main orebody inBeiya mining area; Through the analysis of major and trace element of ore minerals,obtained that the temperature of sulfide metallizing period belong to low mediumtemperature category and it was formed at quartz-sulfurization of skarn formingperiod; and magnetite Ca+Al+Mn-Ti+V and TiO₂-Al₂O₃-MgO plot show that itwas received some sedimentary reformation in late stage.At present, divergent views exist as to the age of Lijiang group （E2l） which is themain occurrence horizon of laterite containing gold. Through palynology research onthe upper and lower part of Lijiang group, this article obtained that the pollen of broadleaved weed and shrubs, grass and herb plant are predominate of this horizon on thewhole, the former content is33.3-44.5%, and the average38.8%; the latter for35.7-38.0%, an average of37.2%. The pollen of acerola plant was secondary, contentis10.4-20.0%, and the average13.1%; the content of ferns spores and algae wererelatively less, from6.4%to12.3%, an average of9.6%. Contrast with pollen work ofprevious researches in adjacent regions like Heqing, Yangyi etc., and combined withthe contact relation of horizon and rock in the mining area, this article preliminaryredefinition that the metallogenic epoch of lateritic gold deposit in Beiya mining areais between Oligocene--early pliocene, the vegetation landscape of metallogenic epochwas mainly forests and grasslands, and the climate of metallogenic epoch was mainlywarmer and wetter subtropical climate, suitable for the development of the lateritic gold deposit.Through the X-ray diffraction and electron microscopic analysis of differentoccurrences of laterite containing gold,we can know that kaolinite+illite+ella stone+limonite+gold is the typomorphic mineral assemblage of the lateritic gold depositin Beiya gold field. Gold exists mainly as native gold and silver gold mine and in theclay minerals （mainly kaolinite） and limonite by mechanical mixing or colloidadsorption.