Linking uplift and mineralisation at the Mount Novit Zn-Pb-Ag Deposit,Northern Australia:Evidence from geology,U-Pb geochronology and sphalerite geochemistry

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.