Geochemistry of the low?grade Early Proterozoic sedimentary sequence in the Pine Creek Geosyncline, Northern Territory

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Abstract
The geochemistry of Early Proterozoic sedimentary rocks from the low‐grade metamorphic terrain W of the South Alligator Hinge Zone in the Pine Creek Geosyncline is reported and discussed in terms of the stratigraphy and differences in rock type. Major element trends are dominated by lithological and mineralogical variations; in particular, the dolomitic nature of pelites in the Mount Partridge and Namoona Groups, the presence of chlorite in Crater Formation pelites, and the volcanic affinity of pelites within the Gerowie Tuff. Concentration of Th, U, Zr, Y, Nb, Ce and La in the clastic sediments of the Finniss River and South Alligator Groups is probably related to the presence of felsic volcanics in these groups; high levels of Sn in these groups may be similarly related, and highlight the apparent volcanogenic source for this metal. The South Alligator Group is a preferred host for base‐metal mineralization, and the regional abundance of several metals in this group enhance its economic potential and support a syngenetic, possibly exhalative, origin for these deposits. Anomalous Co, Ni, and V values in Masson Formation pelites are probably related to the nearby mafic Stag Creek Volcanics. Detrital minerals derived from reworked Archaean basement account for high Zr and Th in the Crater Formation. The geochemical data support the shift in REE patterns related to changes in crustal composition about the Archaean‐Proterozoic boundary, though patterns within the Early Proterozoic have also been influenced by felsic volcanism in the South Alligator Group. The chemical index of alteration (which reflects the degree of weathering of sedimentary rocks) reflects the existence of a major unconformity between the Mount Partridge and Namoona Groups; however, other hiatuses observed in or inferred from the rock record are not evident. The dominant felsic volcanic component of the Gerowie Tuff pelites is also indicated by this technique.