Open File Report 24
The mineralogical and geochemical effects of weathering on volcanics
from the Panglo Deposit, Eastern Goldfields, WA
Profiles above ultramafic and mafic volcanics at Panglo are characterized
by the development of a surficial ferruginous calcrete zone which
is not present above shales. This zone bears Au ~0.05 ppm and is
generally characterized by elevated As, Ba, Cr, Mo, Sb, Sr, V and
Zr contents relative to underlying rocks. Higher levels of Au and
associated elements (As, Mo and Sb) are present directly above Au
mineralization at depth.
Ultramafic rocks generally have high Mg, Cr and Ni contents reflecting
the presence of chlorite-vermiculite and talc through the weathered
profiles. Where weathering is particularly intense, these minerals
may be destroyed and smectitic clays developed. Mafic volcanic profiles
show greater development of micas and hematite than those above
ultramafic rocks. Substantial paragonite is present in the barren
profiles but not in the mineralized profiles.
Within both ultramafic and mafic rocks the mineralization is associated
with elevated levels of S, Ag, As, Co, Mo, Sb, W and Zn. Sometimes
these elements may be found for 5 m vertically above mineralization
in ultramafic profiles. However mineralized mafic volcanic profiles
may have very high levels of As and W for ~50 m above mineralization.
Last updated: Tuesday, January 04, 2000 03:20 PM