CRC LEME
Open File Report 30
ABSTRACT
The mineralogical and geochemical effects of weathering in mafic
and ultramafic profiles, Mt Magnet, WA
Scott, K.M. and Martinez, A.
Material from five drill holes located up to 300 m west of the
Parkinson Pit have provided a suite of mafic volcanic rocks with
which the effects of proximity to mineralization and alteration
in the weathered zone can be determined. Fresh barren rocks consist
of assemblages of calcite + dolomite + albite + chlorite ±
minor mica and more proximal rocks, dolomite + chlorite + paragonite
+ muscovite whereas altered and mineralized assemblages consist
of siderite + dolomite + chlorite + muscovite. With weathering,
the carbonates, chlorite and albite break down to Fe oxides, kaolinite
+ smectites but micas remain essentially unaffected. Thus, within
weathered profiles, increasing proximity to mineralization is reflected
by the progression minor mica -> abundant paragonite + muscovite
-> abundant muscovite i.e. increasing K contents. The relatively
low abundances of other Au pathfinders (As, B, Mo, Sb and W) at
Mt Magnet suggests that high muscovite (or K) contents are probably
the best guide to mineralization in this area.
The absence of talc high in a weathered ultramafic profile suggests,
by comparison with ultramafic profiles from the Eastern Goldfields,
the presence of alteration. This is confirmed by the presence of
some K-rich zones within the profile and elevated abundances of
the Au pathfinders, As, Mo, Sb and Sn, in the surficial calcrete
zone of the profile.
Last updated: Tuesday, January 04, 2000 03:54 PM
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