New discoveries from the Gawler Ranges: Greisen-style mineralisation in Hiltaba Suite granite and a regional stratigraphic marker in the upper GRV
Mario Werner Carmen Krapf, Stacey McAvaney, Ben Nicolson & Mark Pawley
Geological Survey of South Australia Talk Outline
GSSA Projects & Programs • Southern Gawler Ranges Margin Project • Mineral Systems Drilling Program (MSDP) • Role of field mapping in drilling program • What have we done and where can you find it? Recent Discoveries • Greisen-style mineralisation in Hiltaba Suite granite → direct contribution to the understanding of the area’s metallogenetic evolution • Regional stratigraphic marker in the upper GRV → important stratigraphic knowledge for explorers in the GRV region Southern Gawler Ranges Margin Project & Mineral Systems Drilling Program
• Improve geological understanding of GRV-Hiltaba units and underlying basement • Characterisation of various mineral systems associated with GRV-Hiltaba magmatism • Define lithological and structural controls on mineralisation MSDP Drilling and Mapping areas
Six Mile Hill
Peltabinna
Mount Double Role of field mapping in MSDP
• Stratigraphy • Regional vs deposit-scale alteration systems • Constrain interpretation of geophysics • Structural geology and tectonic evolution Field Mapping: documentation and delivery 669 field observations 169 rock samples 62 geochemistry analyses 57 thin sections 13 geochronology samples
available via MSDP Mapping Products Regolith Map Southern GRV Margin
available via Greisen-style alteration and mineralisation in Hiltaba Suite Granite – Pretty Point (Hiltaba) Hiltaba Granite Alteration-Mineralisation Kondoolka Batholith Hiltaba Intrusion (sill)
Hiltaba HS Pretty Point altered Hiltaba Ilkina granite locality Pluton
MSDP07 MSDP05 10 km MSDP06 Hiltaba Granite Alteration-Mineralisation Lake Acraman Yardea Dacite
altered/mineralised granite locality
Hiltaba Intrusion Hiltaba Intrusion granite granite
Pretty Point Camp Ground Hiltaba Granite Alteration-Mineralisation
Copper staining
Qtz-Musc-F-Ht-(bio) Hiltaba Granite Alteration-Mineralisation
15 6 5 3 3 O O
10 2 4 2 3 5 2 wt% Al altered HS granite (Pretty Point) wt% Fe 1 unaltered HS granite 0 0 72 74 76 78 80 72 74 76 78 80
wt% SiO2 wt% SiO2
4 7 6
3 O 5 O 2 2 4 2 3 wt% K wt% Na 1 2 1 0 0 72 74 76 78 80 72 74 76 78 80
wt% SiO2 wt% SiO2 Hiltaba Granite Alteration-Mineralisation
120 200 40 114 ppm 36.6 ppm 100 163 ppm
150 30 80 altered HS granite (Pretty Point) 60 100 20 ppm Bi ppm ppm Sn 40 Cu ppm 50 10 20 unaltered HS granite 0 0 0 72 74 76 78 80 72 74 76 78 80 72 74 76 78 80
wt% SiO2 wt% SiO2 wt% SiO2
250 140 5 120 125 ppm 4.6 ppm 200 197 ppm 4
100 150 80 3 100 60 2 ppm As ppm ppm Zn ppm ppm Pb ppm 40 50 1 20 0 0 0 72 74 76 78 80 72 74 76 78 80 72 74 76 78 80
wt% SiO2 wt% SiO2 wt% SiO2 Hiltaba Granite Alteration-Mineralisation Quartz-muscovite-fluorite-iron oxide rock Alteration characteristics:
radiating muscovite • SiO2 enrichment feldspar replacement fluorite
• Fe2O3 introduction
• Feldspar replacement – muscovite → phyllic alteration
• Fluorite precipitation
Nb anatase, relict bio SEM analysis sulfides • Magnetite destruction
zr • Biotite oxidation
• primary Ti → anatase
TiO2 • base metal mineralisation: cassiterite, chalcopyrite, sphalerite, galena Hiltaba Granite Alteration-Mineralisation Similar Sn ±Pb-Zn-Cu mineralisations related to Hiltaba granite intrusions show elsewhere Au-Ag anomalies: Mincor’s Frog & Bates Prospects: quartz-tourmaline and quartz- limonite veins (same Hiltaba Intrusion as Pretty Point) Earea Dam & Glenloth: Au-Ag in quartz veins associated with anomalous Sn
• Greisen-style alteration/mineralisation seen at Pretty Point could also be prospective for precious metals • Pretty Point forms another expression of multitude of diverse alteration and mineralisation styles within Central Gawler Gold zr Province • Similarities of Pretty Point to greisen alteration and to late-stage magmatic fluid mineral assemblages in Hiltaba microgranite dykes indicate that hydrothermal fluids derived from the crystallising and cooling Hiltaba intrusions played a significant role in the formation of this style of alteration/mineralisation Hiltaba Intrusions DRIVER and SOURCE Regional stratigraphic marker in the upper GRV Mount Friday Formation - volcaniclastic and volcanogenic sedimentary rocks
zr Regional stratigraphic marker in the upper GRV Mount Friday Formation - volcaniclastic and volcanogenic sedimentary rocks
Yardea Dacite (Pondanna Dacite Mb.)
Mount Friday Fm. (Paney Rhyolite Mb.) zr
Eucarro Rhyolite Regional stratigraphic marker in the upper GRV Mount Friday Formation - volcaniclastic and volcanogenic sedimentary rocks
matrix-supported breccias to clast- poor mudstones zr (debris- and mud flow deposits)
clast-supported conglomerates, sandstones and laminated siltstones note local intensive sericite and chlorite alteration of clastic deposits Regional stratigraphic marker in the upper GRV Mount Friday Formation - volcaniclastic and volcanogenic sedimentary rocks
MSDP07: ~90 m of • matrix-supported breccias – mud-rich debris-flow deposits with porphyritic rhyolite clasts • minor sandstone to clast-supported conglomerate, laminated to massive mudstone intervals • no coherent volcanics
zr Regional stratigraphic marker in the upper GRV Mount Friday Formation - volcaniclastic and volcanogenic sedimentary rocks MSDP05: ~30 m of • matrix-supported breccias, laminated or massive mudstones • coherent and autobrecciated porphyritic rhyolite • peperitic (?) intervals
zr Regional stratigraphic marker in the upper GRV Mount Double Ignimbrite – pyroclastic rocks (Allen et al., 2003)
zr Regional stratigraphic marker in the upper GRV Mount Double Ignimbrite – pyroclastic rocks (Allen et al., 2003)
~40 m of flow-banded densely welded rheoignimbrite, partly rich in rhyolitic lithic clasts and pumice clasts, top with alternating crystal-rich/poor ash tuffs
clast-rich facies
rheo-ignimbrite zr
crystal-ash tuffs tube pumice Regional stratigraphic marker in the upper GRV Mount Friday Fm. – Mount Double Ignimbrite – ‘Nonning Sandstone’
Pondanna D.
zr Eucarro R.
Allen et al., 2008 Regional stratigraphic marker in the upper GRV Mount Friday Fm. – Mount Double Ignimbrite – ‘Nonning Sandstone’
Pondanna D.
zr Eucarro R.
Allen et al., 2008 Regional stratigraphic marker in the upper GRV Summary
• Between Eucarro Rhyolite and Yardea Dacite (upper GRV) occurs a lithologically distinct and regionally extensive stratigraphic marker horizon
• Caution! Volcaniclastic rocks are common in lower GRV but not laterally extensive on regional scale zr • Volcaniclastic deposits have provided pathways for hydrothermal fluids → potential for localised stratiform mineralisation in upper GRV
• Does this regionally extensive occurrence of sediments & volcaniclastics in the upper GRV reflect a major significant “event” in the development of the GRV- Hiltaba system? Is there a deeper, underlying tectono-magmatic cause? Disclaimer The information contained in this presentation has been compiled by the Department of State Development (DSD) and originates from a variety of sources. Although all reasonable care has been taken in the preparation and compilation of the information, it has been provided in good faith for general information only and does not purport to be professional advice. No warranty, express or implied, is given as to the completeness, correctness, accuracy, reliability or currency of the materials.
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