Geochemical mapping of the deeply weathered western Yilgarn Craton of Western Australia, using laterite geochemistry

Abstract

Multi-element analysis of ferruginous nodules and pisoliths from lateritic residuum, derived lag and ferruginous gravel, selected from locally derived colluvium (laterite) sampled at an approximate 9 km interval (triangular grid) over the western Yilgarn Craton, shows regional geochemical trends, major lithologies and dispersion halos around significant bedrock mineralization. The sample density (one sample per 60–100 km 2 , depending on sample availability) and extent of the coverage ( c . 400 000 km 2 , including large unsampled areas in drainage) mean that the data are potentially valuable for both exploration and environmental purposes. More than 3100 samples have been analysed for 53 elements by XRF, ICP-AES and ICP-MS, with selected samples also analysed for PGE. Elevated Au abundances in the NE of the survey area not only cluster around known gold deposits but extend beyond them, indicating the likelihood of more widespread mineralization in these areas. A chalcophile element index illustrates potential for Au and base metal mineralization in the westernmost part of the Yilgarn Craton, whereas a pegmatophile index shows a regional NW trend parallel to regional structures. Abundant chromium in granite-dominated areas might indicate mafic-ultramafic remnants (some with anomalous Au) beyond known greenstone belts. A newly discovered regional Hg anomaly trends NW for more than 500 km. Anomalous As, Bi, Mo and Sb along the southern margin of the craton may be related to Au mineralization. The spatial and geochemical consistency of the dataset means that it is well suited to multivariate statistics.

Platinum-group elements in the serpentinite lateritic mantles of the Kongo–Nkamouna ultramafic massif (Lomié region, South-East Cameroon)

“…The high PGE contents notably platinum, palladium and ruthenium reveal that these elements might be sited in some secondary minerals such as Fe-oxides/hydroxides or smectites (Oberthür and Melcher, 2005). Similar observations have been documented in Brazil (Cabral and Lehmann, 2002;Cabral et al, 2008Cabral et al, , 2009 and Australia (Cameron and Hattori, 2005;Cornelius et al, 2008). The weathering blanket of the Nkamouna-Kongo ultramafic complex is characterized by high Eh (0.3-1.11 V) and low pH (3-5).…”

“…Much work has been dedicated to the study of the geochemical behaviour of PGE in laterites (e.g., Bowles et al, 1994;Traoré et al, 2006;Cornelius et al, 2008;Ndjigui, 2008;Ndjigui et al, 2008). According to these authors, platinum-group elements have almost the same behaviour despite their slight content variations in laterites.…”

A continental-scale geochemical atlas for resource exploration and environmental management: the National Geochemical Survey of Australia

“…Some regional geochemical surveys had been carried out in parts of Australia (e.g. Morris et al 1998;Cohen et al 1999;Cornelius et al 2008; the pilot geochemical surveys mentioned above), but no national coverage existed. The modern concept of regional geochemical surveys was first developed last century, and has since proven to be a reliable tool for mineral exploration at various scales (Garrett et al 2008;.…”

Transported cover in northwestern Victoria, Australia — An impediment to geochemical exploration for gold

“…For the HA extraction, which targets the amorphous Mn oxide fraction results of pathfinders were normalized to Mn. The CHI*6 index (As + 3.56 * Sb + 10 * Bi + 3 * Mo + 30 * Ag + 30 * Sn + 10 * W + 3.5 * Se) was developed by Smith and Perdrix (1983) and also tested as it has been effectively used to detect anomalous corridors of chalcophile elements (Cornelius et al, 2008;Smith et al, 1989) using laterite residuum.…”