Lithogeochemical halos and geochemical vectors to stratiform sediment hosted Zn-Pb-Ag deposits Part 2. Rye deposit, McArthur River, Northern Territory

Abstract

The giant stratiform Zn-Pb-Ag HYC deposit displays a broad Zn, Pb and Tl halo which extends laterally along the favourable pyritic black shale facies of the Barney Creek Formation for at least 15 krn west of the deposit. A ferroan dolomite/ankerite halo overlaps with the Zn-Pb-Tl halo extending up to 250 m into the immediate stratigraphic hangingwaD, and 50 to 100 m into the footwall sediments close to the deposit. A manganese carbonate halo is offset from the ferroan dolomite/ankerite halo, being concentrated in the immediate footwall of the deposit and extending laterally along the W-Fold Shale Member. Manganiferous carbonate forms the most pronoW1ced and laterally extensive halo at RYC extending well beyond the Zn-Pb-TI and ankerite halos. The geometry and extent of the halos described above are based on sampling and analyses from two drill holes repolted in this study and a further six drill holes reported previously by I.B. Lambert and K.M. Scott [1. Geochem. Explor. 2, 307-330, 1973]. The SEDEX alteration index previously proposed as a vector for the Lady Loretta deposit [R.R. Large and P.I. McGoldrick, 1998, I. Geochem. Explor. 63, 37-56] has been shown to have applications in the McArthur Basin for defining the favourable stratigraphic unit hosting stratiform Zn-Pb-Ag mineralisation. A modified alteration index (AI Mark 3) has also been developed which eliminates the effect of the shale/dolomite ratio on the index and thus highlights the control of carbonate chemistry and its relationship to stratiform mineralisation. The application of a group of indices including Zn, Pb, Tl, SEDEX alteration index, AI Mark 3 and manganese content of dolomite (MnOd) is proposed for defining the most favourable stratigraphic units for stratiform Zn-Pb-Ag mineralisation within carbonate-bearing sedimentary basins. © 2000 Elsevier Science B.Y. All rights reserved.