A Preliminary Account of Chemical Relationships Between Sulfide Lode and "Banded Iron Formation" At Broken Hill, New South Wales

Abstract

As in many other districts of similar mineralization, the apparently stratiform sulfide orebodies of "Broken Hill type" at and around Broken Hill are almost invariably accompanied by thin beds of iron-rich sedimentary rock, loosely designated "banded iron formation." Representative occurrences of Broken Hill sulfide ore and iron formation have been systematically analyzed as whole rocks, and a preliminary account and comparison of their chemical constitutions is now given. The constitutional evidence supports earlier mineralogical work in indicating quite unequivocally that the two materials are consanguineous. Both show clear relationships between the incidence of "gangue" elements on one hand and of sulfides and oxides on the other. In both cases the major metals show a striking correlation with phosphate (as fluorapatite) and indeed the orebodies and banded iron formations both appear to be localized in phosphatic beds.Assuming, purely as a working hypothesis, that both rock types are of seafloor exhalative/hydrothermal origin (i.e., the result of volcanic or of artesian geothermal brine contributions to the contemporary seafloor), their el.emental constitutions are used to deduce possible sedimentary conditions under which the relevant precipitates were deposited. It is suggested that whether a particular exhalative episode led to the formation of sulfide ore or of banded iron formation depended on the rate and scale of emission of exhalative fluids and hence on the degree to which the latter modified the seafloor environment, and, in a qualitative way, on variation in composition of the exhalations related to differences in intensity of exhalative-hydrothermal activity from one episode to another.

The Zn-Pb-(Ag) Deposits Huaripampa and Carahuacra in the Mining District of San Cristóbal, Central Peru

“…Measurements on Pb isotopes in samples of galena from Huaripampa and Carahuacra show Ph-isotopic ratios which are close to those of the orogenic growth curve (Gunnesch and Baumann 1986;Fontbote et al, this Vol.). Similar observations were also made on Ph-isotopic measurements on other stratiform Pb-Zn deposits (Stanton 1972a;Large 1980;Gustafson and Williams 1981). 7.…”

“…5. The presence of banded ironstones as they also occur in other stratiform Pb-Zn deposits (Anhaeuser and Button 1976;Stanton 1972b;Stanton and Vaughan 1979;Derry et al 1965;Saif 1980). 6.…”

A metamorphogenic alteration zone around the stratiform Broken Hill ore deposits, Australia.

“…Many workers (inter alia RAMDOHR, 1950;KING, 1958;SEGNIT, 1961;CARRUTHERS, 1965;LAWRENCE, 1967;STANTON, 1972;BOTH, 1973;HODGSON, 1974) have suggested that the orebodies have been metamorphosed to a high grade with the enclosing host rocks and were probably originally stratiform.…”

Fluctuations in a magmatic sulphur isotope signature from the Pinnacles Mine, New South Wales, Australia

“…The source of the ore-forming fluids is a point of current debate: many workers support a volcanic-exhalative model for the formation of the ores (e.g. Stanton 1972;Plimer 1979;Willis et al 1983) in which hydrothermal ore fluids are derived from magmatic and meteoric sources. Other models favour a sedimentary-exhalative origin for the ores because of the lack of any recognisable footwall stockwork zone and the predominance of metasedimentary over metavolcanic rocks in the orebearing sequence and in the overlying rocks (e.g.…”

“…The succession include several hundred small base metal sulphide deposits, as well as the giant Willis et al 1983). Several sulphur isotope studies have been undertaken for the Broken Hill ores (Stanton andRafter 1966, 1967;Both and Smith 1975;Spry 1987), Broken Hill-type mineralisation (Both and Smith 1975) and vein-type mineralisation elsewhere in the Willyama Supergroup (Dong et al 1987). 634S values for the Broken Hill ores and for Broken Hill-type mineralisation show a fair degree of consistency and cluster around, or are slightly greater than 0%oo.…”