Abstract:

Quartz,bitumem,prehniteandCu-bearingmineralswidelyoccurinamygdaloidbasalticdrusefromPugecounty,south Sichuan. According to their occurrences and relationships, three types of basaltic druse are divided: quartz-bitumen druse, rock crystal-bitumendruse,rockcrystal-prehnitedruse.Themineralassemblagesfromrockcrystal-prehnitedrusedisplaythefeatureof nodules, which outward include prismatical rock crystals, prehnite spherulites and Cu-bearing minerals spherulites. Moreover, Cu-bearingmineralsspheruliteshavethefeatureofcirclelayeredstructure,includingnativecopper(core),tenorite(mantle)and chalcostaktite-malachite(crust).Observationsinfieldandundermicroscopeshowthattheshapesandoccurrencesofnativecopper controlthepatternoftheCu-bearingmineralsaggregations.Cu-bearingmineralsspherulitesaremainlydistributedintheconvergences amongtheprehnitespherulites,andthecoreisgranularnativecopper.Cu-bearingmineralsveinsincludestretchnativecopper, tenorite,chalcostaktite,occurinthefracturesofdruses.Thecarbonisotopeandinfraredspectrumsuggestthatasphaltisofbiogenesis andoriginatedfromthecarbonaterocksinPermianstrata(P13).Themineralsinbasalticdrusescrystallizedfromtheorganicfluids,the
commonly recognized sequence is chalcedony → quartz + bitumen+ native copper → native copper + prehnite → tenorite → chalcostaktite→malachite→calcite.Thespiralgrowthpatternsofbitumen,homogenizationtemperatureofinclusionsinquartzand therelationshipsbetweenbitumenandnativecopperinrockcrystalindicatethatbitumenformedunderthethermalcrackingoforganic (crudeoil),thetemperatureis290-230℃.Nativecoppercrystallizedunder230-160℃.

Key words:  typesofdrus;bitumenandnativecopper;rockcrystalandprehnite;shapeandoccurrences;compositionandinfra-red spectrum;genesis;PugecountyinsouthSichuan