Abstract
Ph.D. (Geology)
Shear zone controlled hydrothermal alteration zones in the
northern Kaapvaal craton (NKC) are developed in host rocks of
vastly different chemical composition and metamorphic grade.
Some carry appreciable Au and base metals and some are
barren. Alteration zones in three different distinctive
crustal zones were examined in detail to determine the
controls of these two types of alteration.
1. The Matok Complex is situated in the southern marginal
zone (SMZ) of the Limpopo Belt (LB), close to the zone of
rehydration. Two major stages of hydrothermal alteration
could be identified in local shear zones, a pervasive
propylitization and a subsequent vein controlled quartzalbite
alteration. The two-stage alteration occurred
sometimes between the emplacement of the Matok Complex (2670
Ma) and the intrusion of unaltered mafic dykes (1900 Ma).
Calculated isotopic compositions of the hydrothermal fluids
indicate that magmatic ± meteoric waters as well as juvenile
C02 were responsible for the establishment of the alteration
zones. The fluids most probably were late magmatic fluids
associated with the Matok magmatism. The propylitic
alteration was accompanied by introduction of small amounts
of CU + Au and represents an alteration type identical to
that developed in porphyry copper deposits. The subsequent
quartz-albite alteration was caused by extremely saline
fluids which depleted the rocks of all the major and trace
elements with exception of Si, Al, Na and Zr.
2. This chemical alteration pattern' contrasts with those
developed in two alteration zones associated with economic
gold mineralization in greenstone belts of the NKC
(Sutherland and Pietersburg belts). At the Birthday and
Eersteling gold mines, a biotite-calcite-quartz alteration is
developed. The chemical pattern of the alteration is...