| Abstract |
The majority of hydrothermal minerals in the Tongonan field occur as: 1) p a r t i a l replacement of groundmass and phenocrysts (disseminated mi-neralisation) and 2) in filling or lining of vugs, cavities nnd fractures (vein mineralisation. These minerals exhibit a distinct and systematic distribution with depth and temperature. The opaque minerals comprise three vblume per cent of the rocks, but locally reach fifteen percent in the intrusive contact and in the acid alteration zones. Pyrite dominates in most zones except in the R- silicate zones where a preponderance of magnetite over pyrite has been observed. Cenetically,the opaques can be divided into: mamatic(magnetite, yrrhotite , ilmenite, chromit :, ti tanomagne ti t e 7, sed imentary/diaqenetic ( pyrite, hematite, maghemite , contact metaand hyoTene!sphalerite, galena, chalcopyrite, borni e, pyrite) minerals. A temprature and distinct zonation of opaque minerals also parallels the calc-silicatealte ration zones. Chalcopyrite is the most abundant base-metal sulphide. Ninor t o trace galena first appears in the inter-kyered illite-montmorillonite sub-zone and persists with drilled depths; it is also strongly associated with hematite in acid alteration zones. Sphalerite is more intimately related with the propylitic alteration assemblage. Kagnetite and pyrrhotite occur as ubiquitous inclusion in pyrite. Tn zones peripheral to dykes 'and in the main transition or ticontact" zone, rna.;netite exhibits a preponderance over pyrite . This local abundLmce coincides with the !<-silicate and advanced propylitic zones. |