Geochemistry of Kalgoorlie Gold Deposits. A seminar presented by; Sponsored by;

Size: px

Start display at page:

Download "Geochemistry of Kalgoorlie Gold Deposits. A seminar presented by; Sponsored by;"

Lucas Sherman
5 years ago
Views:

1 Geochemistry of Kalgoorlie Gold Deposits. A seminar presented by; Sponsored by;

2 Spectral Mineralogy in Yilgarn Gold Deposits 26 th July 2017

3 What happens to syn-volcanic alterations systems during metamorphism? Smectite-Chlorite-Calcite alteration in basalt is converted to paragonite-chlorite- (chloritoid) at middle greenschist, and clinozoisite-albite at upper greenschist. The largest footprints of paragonite in the Yilgarn are around Wallaby, and around the Golden Mile. Jupiter Wallaby Paragonite

4 Spectral mineralogy case study. Backflip vein, 3km west of Mt Pleasant Backflip Lady Bountiful Quarters Racetrack

5 Backflip vein case study Hydrothermal chlorite with symmetric Fe-OH, Mg-OH features FSFR.2077 Int=3.0 sec Depth Norm. HullQ Wavelength in nm 0.001

6 Backflip vein case study Chlorite with asymmetric Fe-OH, Mg-OH features FSFR.2077 Int=3.0 sec Depth Norm. HullQ Wavelength in nm 0.001

7 Backflip vein case study White Mica with variable Al-OH wavelengths FSFR.2077 Int=3.0 sec Depth Norm. HullQ Wavelength in nm 0.001

8 Backflip vein case study Mixtures of white mica and chlorite FSFR.2077 Int=3.0 sec Depth Norm. HullQ Wavelength in nm 0.001

9 Backflip vein case study Supergene clays in the weathering profile, kaolinite (+ smectite and Fe-oxides) FSFR.2077 Int=3.0 sec Depth Norm. HullQ Wavelength in nm 0.001

10 Backflip vein case study Chlorite compositions For the chlorite-bearing samples, plot depth of the Fe-OH feature versus depth of the Mg- OH feature; this is bimodal. The hydrothermal chlorite is symmetrical. The metamorphic chlorite is asymmetric.

Backflip vein case study White mica compositions Muscovite-chlorite Phengite Paragonite-chlorite Kaolinite, montmorillonite (+/- chlorite) Plot the wavelength of the Al-OH feature versus width of

11 Backflip vein case study White mica compositions Muscovite-chlorite Phengite Paragonite-chlorite Kaolinite, montmorillonite (+/- chlorite) Plot the wavelength of the Al-OH feature versus width of the Al-OH feature; this is a really useful plot for picking mixtures with supergene clays. There is a range of 20nm in the wavelength of the Al-OH feature. Paragonite forms a discrete population.

12 Backflip vein case study Mineralogy is zoned around the vein from sericite to sericite+chlorite to hydrothermal chlorite, with background metamorphic chlorite

13 Backflip vein case study White mica compositions are zoned from phengite in the north to muscovite in the center and paragonite to the south

14 Backflip vein case study White mica compositions along the plane-of-the-vein phengite Barren paragonite zone muscovite paragonite High grade shoot, muscovite

15 White Mica Compositions In terms of spectral signatures, there is a continuum from phengite to muscovite to paragonite 2194nm Norm. HullQ (Stacked) Mica Composition, samples 1 to 9 (Aux colour: Index) 2218nm Wavelength in nm Aux NULL

16 Phengite component in sericite from EMP analyses plotted against 2200nm wavelength from PIMA; (Fe + Mg) calculated on a K 2 Al 6 Si 6 O 20 (OH) 4 unit formula basis.

White Mica Compositions Kanowna Belle, sericite-albite-pyrite-ankerite. K/Al vs Na/Al molar ratio plot coloured by Al-OH wavelengths. 2KAl 2 (AlSi 3 )O 10 (OH) 2 (musc) + K + + 1.5Fe 2+ +4.

17 White Mica Compositions Kanowna Belle, sericite-albite-pyrite-ankerite. K/Al vs Na/Al molar ratio plot coloured by Al-OH wavelengths. 2KAl 2 (AlSi 3 )O 10 (OH) 2 (musc) + K Fe SiO 2 +3H 2 O 3KFe 0.5 Al 2 (Al 0.5 Si 3.5 )O 10 (OH) 2 (phen) + 4H + Points on the muscovite-albite tie-line have a short wavelength; points above the tie-line have a long wavelength. This is a ph dependent substitution. Compositionally, there is a continuum between muscovite and phengite. There is NOT a continuum between muscovite and paragonite.

18 White Mica Compositions Paragonite-Muscovite solid solution diagram. In SWIR spectra there is a continuum between muscovite and paragonite. Chemically, muscovite and paragonotite represent VERY different chemical environments. 600 Muscovite composition Paragonite composition 500 Temp o C Immiscibility gap 200 K Na KAl 2 (AlSi 3 )O 10 (OH) 2 NaAl 2 (AlSi 3 )O 10 (OH) 2

19 White Mica Compositions Data from Mt Pleasant; whole rock analyses of mica-bearing samples. The indigo points are samples with intense paragonite-chlorite alteration, hosted in basalt. The alteration has NOT changed the bulk composition of the rock. These have very anomalous Sb-Cs-Li. Paragonite-Fe chlorite is a metamorphic assemblage formed from smectite-chlorite-calcite alteration in basalt. Projected position of unaltered basalt

20 Backflip vein case study Rather than a N-S lateral zoning, Backflip is a system that was tilted after formation; it was zoned from bottom to top, with clay alteration formed above the gold shoot. phengite muscovite Barren paragonite zone paragonite High grade shoot, muscovite

21 CSIRO Superpit HyLogger trial Plot the wavelength of the Al-OH feature versus width of the Al-OH feature; Use a point density contour overlay. Note the discrete population of paragonite-bearing rocks around 2190nm. Muscovite Phengite Paragonite-chlorite

22 CSIRO Superpit HyLogger trial Gridded image of gold assays in RC grade control data overlain by spectral mineralogy. The Fimiston lodes are strands of muscovite in a sea of paragonite + Fe-chlorite.

23 CSIRO Superpit HyLogger trial Gridded image of white mica Al-OH wavelength in RC grade control data overlain by spectral mineralogy.

24 Image from Tom Cudahy, CSIRO Superpit HyMap The dark blue is paragonite, not muscovite! Fimiston Lodes had proximal illite in a background of smectite.

25 Regional Spectral Map Pick the palaeo-clay zones in mafic rocks. Mt Pleasant Kanowna Belle Gidji 10km Binduli Golden Mile

26 2670 to 2660Ma shallow level alteration. Clay alteration in mafic rocks is metamorphosed to paragonite-fe chlorite-chloritoid at middle greenschist, clinozoisite-albite at upper greenschist Illite- Smectite Smectite Chlorite- Smectite Paragonite-Fe chlorite +/- Chloritoid Middle greenschist Biotite Clinozoisite -Albite Upper greenschist

3D model of a Supergene Gold Deposit derived from Spectral Mapping

3D model of a Supergene Gold Deposit derived from Spectral Mapping Exploration Technologies 2011 Scott Halley ABSTRACT: A 3D MODEL OF A SUPERGENE GOLD DEPOSIT CREATED FROM SPECTRALLY DERIVED MINERALOGY