Bk. Townley et al., Base and precious metals geochemistry of rock units of the mainland Aysen region, Chilean Patagonia, J GEOCHEM E, 68(1-2), 2000, pp. 21-46
In order to evaluate the applicability of regional rock geochemistry as an
aid in mineral exploration, over 1000 rock chip samples of the Aysen region
, Chile, were taken during the period 1993-1995. All samples were analyzed
at commercial laboratories for 30 elements by induced coupled plasma atomic
emission spectrometry (ICP-AES), and in addition, Au was determined by ato
mic absorption spectrometry (AAS). Rock samples were classified into two br
oad groups: (1) unaltered unmineralized rocks; and (2) altered and minerali
zed rocks. The geologic-tectonic setting of the area is a segment of the ac
tive continental margin of South America where, during the Late Jurassic an
d Cretaceous, a magmatic are developed accompanied by an easterly marine ba
ck-are basin. The basement is formed of Paleozoic metamorphic rocks that ar
e interpreted as sedimentary wedges accreted to the Gondwana continent. The
back-are basin was filled by the end of the Mesozoic, and Tertiary volcani
c and terrestrial sedimentary rocks that represent local basins and within-
plate volcanism lie uncomformably on older units. The main mineralization i
n the region is coeval with Late Jurassic-Cretaceous magmatism and this is
consistent with the geochemical data presented in this paper. Younger rocks
show low geochemical values, suggesting that the change of tectonic regime
by the end of the Mesozoic resulted in limited mineralizing processes duri
ng the Tertiary in the region. The regional rock geochemistry shows that un
altered unmineralized rock units of this region are well within global mean
ranges for similar rock types, excepting As, which exhibits a conspicuous
positive anomaly for most rock types. Altered and mineralized rock geochemi
stry and statistical treatment of data suggest potential for polymetallic m
ineralization in the region, the most prospective rock units being the volc
anic Mesozoic rocks. (C) 2000 Elsevier Science B.V. All rights reserved.