The subeconomic Mount Novit Zn-Pb-Ag deposit is located approximately 20 km south of Mount Isa,Queensland.In contrast to the nearby Mount Isa,Hilton and George Fisher Zn-Pb-Ag deposits,mineralisation at Mount Novit is...The subeconomic Mount Novit Zn-Pb-Ag deposit is located approximately 20 km south of Mount Isa,Queensland.In contrast to the nearby Mount Isa,Hilton and George Fisher Zn-Pb-Ag deposits,mineralisation at Mount Novit is situated to the west of the regional-scale Mount Isa Fault and is hosted in the Moondarra Siltstone as opposed to the Urquhart Shale.Lower-grade(<4 wt.%Zn+Pb)Zn-Pb-Ag mineralisation primarily replaces pre-existing carbonate alteration and veining and consists of pyrrhotite,pyrite and sphalerite with lesser galena.Higher-grade(>10 wt.%Zn+Pb)mineralisation occurs as a matrix supported breccia dominated by sphalerite and pyrrhotite with galena,pyrite,and magnetite.In-situ U-Pb geochronology was completed on apatite and two textural varieties of monazite.Fine-grained(<50μm)subhedral to anhedral monazite is located within highly foliated biotite alteration directly adjacent Zn-Pb-Ag mineralisation and yields a mean weighted^(207)Pb/^(206)Pb age of 1527±18 Ma(MSWD=1.06).This age is consistent with the formation of highly foliated biotite alteration during D;deformation of the Isan Orogeny.Apatite from the same fabric yields a lower intercept age of1443±29 Ma(MSWD=1.30).Consistent with previous studies,this age is interpreted to represent the age of a major thrusting event along the Mount Isa Fault that resulted in the cooling of the Mount Novit area below~375℃.Coarse-grained monazite is coeval with Zn-Pb-Ag mineralisation and yields a mean weighted^(207)Pb/^(206)Pb age of 1457±11 Ma(MSWD=0.28).Sphalerite from Mount Novit has low concentrations(<1 ppm)of Ge and Ga and a relatively high concentration of In(5 to>10 ppm),possibly reflecting the leaching of the metals from an underlying basement unit.The GGIMFis geothermometer(Frenzel et al.,2016)produced a mean formation temperature of 345±52℃.The timing and temperature of Zn-Pb-Ag mineralisation is consistent with the age and cooling temperature of apatite presented in this study.Based on these correlations,we suggest that Zn-Pb-Ag mineralisation at Mount Novit was emplaced during an episode of major thrusting along the Mount Isa Fault,with the precipitation of Zn-Pb-Ag mineralisation driven by the cooling of the Mount Novit area below~375℃.A key implication of this study is a new model for synorogenic Zn-Pb-Ag mineralisation to the south of Mount Isa,which contrasts with the widely accepted regional-scale syngenetic metallogenic model.展开更多
基金supported by the Australian Government Research Training Programfunded by Mount Isa MinesDa Glencore Company and forms part of the Mount Isa Research for Geology and Exploration(MIRGE)project。
文摘The subeconomic Mount Novit Zn-Pb-Ag deposit is located approximately 20 km south of Mount Isa,Queensland.In contrast to the nearby Mount Isa,Hilton and George Fisher Zn-Pb-Ag deposits,mineralisation at Mount Novit is situated to the west of the regional-scale Mount Isa Fault and is hosted in the Moondarra Siltstone as opposed to the Urquhart Shale.Lower-grade(<4 wt.%Zn+Pb)Zn-Pb-Ag mineralisation primarily replaces pre-existing carbonate alteration and veining and consists of pyrrhotite,pyrite and sphalerite with lesser galena.Higher-grade(>10 wt.%Zn+Pb)mineralisation occurs as a matrix supported breccia dominated by sphalerite and pyrrhotite with galena,pyrite,and magnetite.In-situ U-Pb geochronology was completed on apatite and two textural varieties of monazite.Fine-grained(<50μm)subhedral to anhedral monazite is located within highly foliated biotite alteration directly adjacent Zn-Pb-Ag mineralisation and yields a mean weighted^(207)Pb/^(206)Pb age of 1527±18 Ma(MSWD=1.06).This age is consistent with the formation of highly foliated biotite alteration during D;deformation of the Isan Orogeny.Apatite from the same fabric yields a lower intercept age of1443±29 Ma(MSWD=1.30).Consistent with previous studies,this age is interpreted to represent the age of a major thrusting event along the Mount Isa Fault that resulted in the cooling of the Mount Novit area below~375℃.Coarse-grained monazite is coeval with Zn-Pb-Ag mineralisation and yields a mean weighted^(207)Pb/^(206)Pb age of 1457±11 Ma(MSWD=0.28).Sphalerite from Mount Novit has low concentrations(<1 ppm)of Ge and Ga and a relatively high concentration of In(5 to>10 ppm),possibly reflecting the leaching of the metals from an underlying basement unit.The GGIMFis geothermometer(Frenzel et al.,2016)produced a mean formation temperature of 345±52℃.The timing and temperature of Zn-Pb-Ag mineralisation is consistent with the age and cooling temperature of apatite presented in this study.Based on these correlations,we suggest that Zn-Pb-Ag mineralisation at Mount Novit was emplaced during an episode of major thrusting along the Mount Isa Fault,with the precipitation of Zn-Pb-Ag mineralisation driven by the cooling of the Mount Novit area below~375℃.A key implication of this study is a new model for synorogenic Zn-Pb-Ag mineralisation to the south of Mount Isa,which contrasts with the widely accepted regional-scale syngenetic metallogenic model.
