Lead isotope signatures of stratiform and strata-bound mineralization in the Broken Hill Block, New South Wales, Australia

The geology, SHRIMP U–Pb geochronology and metallogenic significance of the Ankisatra-Besakay District, Andriamena belt, northern Madagascar

“…BHT districts are commonly characterised by their: (1) intracratonic rift basin setting; (2) upper amphibolite-to granulite-facies metamorphism, with strong metasomatic overprints; (3) multiple episodes of deformation and magmatism; and (4) unique transitional lode horizons (Gulson et al, 1985;Kerr, 1994). Debate on the genesis of BHT deposits highlights two main controversial models: (1) the syn-to post-metamorphic, magmatic-hydrothermal origin; and (2) the syn-sedimentary or diagenetic model (Giles and Ehlers, 1997).…”

“…The syn-sedimentary model suggests erosion and accumulation of base metals from the syn-rifting quartz-feldspar basement rocks (Gulson et al, 1985;Sawkins, 1989;Stevens et al, 1990;Solomon and Groves, 1994).…”

“…Isa Block and the Bushmanland Ore District are largely outlined from Gulson et al (1985), Ryan et al (1986), Joubert (1986, Skrzeczynski (1993), Solomon and Groves (1994), Kerr (1994), AGCRC (1995), Walters (1996), Willis (1996), Giles and Ehlers (1997) and Reid et al (1997). BHT districts typically display the following features:…”

“…Thin siliceous units, magnetic lode horizons, including BIF, calc-silicate units, gahnite quartzite and other unusual chemical sedimentary rocks, and most importantly BHT stratiform/stratabound PbZn-Ag deposits, typify these transitional sequences. There are narrow, small-scale cross-cutting mineralised veins and shear zones in these BHT Provinces (Gulson et al, 1985;Reid et al, 1997). Based on Pb-isotope data, vein-type Pb-Zn-Ag deposits in some of these provinces are shown to be genetically related to giant stratiform/stratabound Pb-Zn-Ag deposits (e.g.…”

“…Based on this knowledge, it is possible that vein-type mineralisation in potential BHT provinces could be used as pathfinders for locating giant stratiform/stratabound deposits, which may have been structurally relocated at depth or along strike during polydeformation events. However, in the world-class BHT Provinces of Broken Hill Main Lode in New South Wales, and the Cannington deposit in Queensland, Australia, stratiform/ stratabound Pb-Zn-Ag deposits are not apparently genetically linked to the cross-cutting mineralised veins and shear zones, at least based on Pb-isotope signatures (Gulson et al, 1985;Stevens et al, 1990), so Pb-isotope data are equivocal. In addition to the Palaeoproterozoic and Mesoproterozoic orogenic belts, some analogous, but much smaller and less economic BHT deposits have been recognised in younger mobile belts (e.g.…”