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Albite-rich sedimentary rocks that contain abundant Fe sulphides occur in the lower portion of the ultramafic sequence at Kambalda and their broadly antipathetic relationship to most of the nickel orebodies is well documented. These sediments generally contain less than 0.1% Ni, but nickeliferous equivalents with 0.3 to >6% Ni occur locally in close spatial association with more typical volcanic peridotite-associated massive, matrix and disseminated ores. Nickeliferous sediments have been mined at several locations at Kambalda but, collectively, they constitute less than 2% of the total Kambalda nickel reserve.The nickeliferous sediments occur both on the ultramafic-footwall basalt contact and within the lower part of the ultramafic sequence, and are usually less than 5 m thick. They are commonly finely laminated rocks with a cherty appearance, composed essentially of layers of albite+quartz±amphibole, alternating with pvrrhotite+pentlandite±pyrite layers. Some contain a minor amount of carbon. The sediments are only of ore grade (> 1% Ni) immediately adjacent to massive Fe-Ni-Cu sulphides, which are interpreted as normal magmatic ores on the basis of geochemistry and the presence of distinctive ferrochromites. The nickel content of the sediments decreases to background levels (<0.1%) within about 20 m of the massive sulphides. In most locations the massive sulphides clearly have been emplaced tectonically within or adjacent to the sediments, which are commonly highly deformed. Typical nickeliferous sediments contain about 1% Ni, 0.1% Cu, 0.1% Zn, 400 ppb Pd, <0.2 ppb Ir and 10-200 ppb Au. They have lower Ni/Cu (average 10), higher S/Ni (average 6) and higher S/Se (average 11 200) than associated massive sulphides (average 40, 4.8 and 7400, respectively). The Pd/Ir ratio of the nickeliferous sediments (typically > 1000) contrasts markedly with that of associated massive sulphides (average ca 16). The high Pd/Ir values are similar to those which have been reported fo, Albite-rich sedimentary rocks that contain abundant Fe sulphides occur in the lower portion of the ultramafic sequence at Kambalda and their broadly antipathetic relationship to most of the nickel orebodies is well documented. These sediments generally contain less than 0.1% Ni, but nickeliferous equivalents with 0.3 to >6% Ni occur locally in close spatial association with more typical volcanic peridotite-associated massive, matrix and disseminated ores. Nickeliferous sediments have been mined at several locations at Kambalda but, collectively, they constitute less than 2% of the total Kambalda nickel reserve.The nickeliferous sediments occur both on the ultramafic-footwall basalt contact and within the lower part of the ultramafic sequence, and are usually less than 5 m thick. They are commonly finely laminated rocks with a cherty appearance, composed essentially of layers of albite+quartz±amphibole, alternating with pvrrhotite+pentlandite±pyrite layers. Some contain a minor amount of carbon. The sediments are only of ore grade (> 1% Ni) immediately adjacent to massive Fe-Ni-Cu sulphides, which are interpreted as normal magmatic ores on the basis of geochemistry and the presence of distinctive ferrochromites. The nickel content of the sediments decreases to background levels (<0.1%) within about 20 m of the massive sulphides. In most locations the massive sulphides clearly have been emplaced tectonically within or adjacent to the sediments, which are commonly highly deformed. Typical nickeliferous sediments contain about 1% Ni, 0.1% Cu, 0.1% Zn, 400 ppb Pd, <0.2 ppb Ir and 10-200 ppb Au. They have lower Ni/Cu (average 10), higher S/Ni (average 6) and higher S/Se (average 11 200) than associated massive sulphides (average 40, 4.8 and 7400, respectively). The Pd/Ir ratio of the nickeliferous sediments (typically > 1000) contrasts markedly with that of associated massive sulphides (average ca 16). The high Pd/Ir values are similar to those which have been reported fo

The Olympic Dam breccias are interpreted to have been generated by a variety of processes, including: hydrothermal and phreatomagmatic explosive mechanisms, fault-related dilatancy and cataclasis, epiclastic sedimentation and chemical corrosion with resultant textural collapse. Early fault activity probably played a significant role in determining the initial distribution of hydrothermal centres and the overall morphology of the entire system. The hydrothermal centres evolved into a complex array of variably mineralised, lenticular, pipe-like and irregularly shaped breccia bodies as a result of on-going brecciation, alteration, mineral precipitation and fault activity. Mafic and felsic magmas invaded the active hydrothermal system, producing phreatomagmatic explosions and localised diatreme structures. The system appears to have repeatedly vented at the surface, creating a composite, nested eruption/collapse crater. The resulting epiclastics, consisting of reworked hydrothermal eruption breccias and Gawler Range Volcanics volcaniclastics, accumulated in this crater complex and were subsequently incorporated into the underlying breccias by collapse and subsidence. Localised layering developed within subsurface breccias as a result of hydrothermal processes., The Olympic Dam breccias are interpreted to have been generated by a variety of processes, including: hydrothermal and phreatomagmatic explosive mechanisms, fault-related dilatancy and cataclasis, epiclastic sedimentation and chemical corrosion with resultant textural collapse. Early fault activity probably played a significant role in determining the initial distribution of hydrothermal centres and the overall morphology of the entire system. The hydrothermal centres evolved into a complex array of variably mineralised, lenticular, pipe-like and irregularly shaped breccia bodies as a result of on-going brecciation, alteration, mineral precipitation and fault activity. Mafic and felsic magmas invaded the active hydrothermal system, producing phreatomagmatic explosions and localised diatreme structures. The system appears to have repeatedly vented at the surface, creating a composite, nested eruption/collapse crater. The resulting epiclastics, consisting of reworked hydrothermal eruption breccias and Gawler Range Volcanics volcaniclastics, accumulated in this crater complex and were subsequently incorporated into the underlying breccias by collapse and subsidence. Localised layering developed within subsurface breccias as a result of hydrothermal processes.

The Vulcan prospect, a newly discovered Cu-Au prospect located within the eastern Gawler craton of South Australia, is entirely subsurface and defined by a geophysical anomaly intersected by diamond drilling. Eight drill holes have all intersected haematite-rich alteration and Cu-Au mineralisation within a variety of breccia types ranging from those composed entirely of hydrothermal haematite + sericite + chlorite to those dominated by altered rock in which clasts of protolith rock are preserved. The highest-grade zones of mineralisation at Vulcan occur within haematite-dominant breccias. Molybdenite within haematite-rich brecciated granite samples has been dated via the Re-Os method and yields a crystallisation age of 1 586 +/-8 Ma (including decay constant uncertainties). SHRIMP zircon U-Pb analysis shows that a sample of haematite-sericite-chlorite-altered and brecciated granite was emplaced at 1 743 +/-7 Ma. The new data from Vulcan confirm that haematite breccia-related Cu-Au mineralisation formed during a widespread alteration and mineralisation event between c.1 600 and 1 570 Ma, broadly coeval with the voluminous felsic large igneous province of the Gawler Range volcanics/Hiltaba suite, and are consistent with most interpretations of the geology of the Olympic Cu-Au province., The Vulcan prospect, a newly discovered Cu-Au prospect located within the eastern Gawler craton of South Australia, is entirely subsurface and defined by a geophysical anomaly intersected by diamond drilling. Eight drill holes have all intersected haematite-rich alteration and Cu-Au mineralisation within a variety of breccia types ranging from those composed entirely of hydrothermal haematite + sericite + chlorite to those dominated by altered rock in which clasts of protolith rock are preserved. The highest-grade zones of mineralisation at Vulcan occur within haematite-dominant breccias. Molybdenite within haematite-rich brecciated granite samples has been dated via the Re-Os method and yields a crystallisation age of 1 586 +/-8 Ma (including decay constant uncertainties). SHRIMP zircon U-Pb analysis shows that a sample of haematite-sericite-chlorite-altered and brecciated granite was emplaced at 1 743 +/-7 Ma. The new data from Vulcan confirm that haematite breccia-related Cu-Au mineralisation formed during a widespread alteration and mineralisation event between c.1 600 and 1 570 Ma, broadly coeval with the voluminous felsic large igneous province of the Gawler Range volcanics/Hiltaba suite, and are consistent with most interpretations of the geology of the Olympic Cu-Au province.

Studies of selected elements in the ores and wall rocks at the Rosebery deposit indicate the presence of three elemental suites. These are: (1) elements concentrated in the upper portions of the orebody and in the adjacent wall rocks (Pb, Zn, Au, Ag, Cd and Sb); (2) elements concentrated in the lower portions of the orebody and adjacent wall rocks (Cu, Bi, As and Fe); and (3) elements dispersed well outside zones of strong mineralisation (Tl and Hg). These groupings are the result of different physicochemical conditions in the ore-forming environment. Group (1) elements were deposited under lower temperature conditions (about 250 degrees C) in response to either a decrease in temperature or an increase in fO2. Group (2) elements were deposited at higher temperatures (about 300 degrees C) in response to a decrease in temperature or an increase in pH. Tl was deposited either by oxidation of H2S or by adsorption onto clay minerals in the wall rock., Studies of selected elements in the ores and wall rocks at the Rosebery deposit indicate the presence of three elemental suites. These are: (1) elements concentrated in the upper portions of the orebody and in the adjacent wall rocks (Pb, Zn, Au, Ag, Cd and Sb); (2) elements concentrated in the lower portions of the orebody and adjacent wall rocks (Cu, Bi, As and Fe); and (3) elements dispersed well outside zones of strong mineralisation (Tl and Hg). These groupings are the result of different physicochemical conditions in the ore-forming environment. Group (1) elements were deposited under lower temperature conditions (about 250 degrees C) in response to either a decrease in temperature or an increase in fO2. Group (2) elements were deposited at higher temperatures (about 300 degrees C) in response to a decrease in temperature or an increase in pH. Tl was deposited either by oxidation of H2S or by adsorption onto clay minerals in the wall rock.