Hi @salpetie ,
I've just finished reading one of the academic papers that you linked from Novo's website.
http://novoresources.com/_resources...and-meallogenesis-the-case-for-syngenesis.pdf
One of the main mysteries discussed in this paper is where did all the gold come from to form the WWR and the answer is here in this passage.
‘‘The main problem lies in accounting for the sheer
quantity of not only the gold but also of the pyrite and uraninite in the
placers.’’ Indeed, any case against the wholesale detrital derivation of
gold in particulate form from the hinterland that is formulated on the
basis of the immense tonnage involved grows with the realization that
even supposing that ;39,000 t of gold remain to be recovered
(Frimmel and Minter 2002, p. 17), there likely remains at least an
equivalent amount of unpayable gold ‘‘reserves’’ in excess of the
estimated 2 3 50,000 t ultimately recoverable. Other workers (e.g.,
Reimer 1975, 1984; Pretorius 1991) have also argued that there is too
much particulate gold in the WWR conglomerates to have been
entirely derived by detrital processes from a ‘‘fertile’’ hinterland rich in
hydrothermal gold deposits. In contrast, Loen (1992) calculated that
the total gold embedded in the WWR could easily have been derived by
weathering of a source exhibiting no unusual concentrations of gold.
Note, however, that such gold would be present mainly as chemically
dissolved gold and/or as minute inclusions in various minerals. This
‘‘chemical’’ gold—transported in solution or as colloids to the edge of
the WWR basin—would have to have been transformed into grains of a
size amenable to mechanical emplacement as a placer. The most likely
loci of transformation would have been shallow-water environments
along the basin edge in which bacteria thrived. These would be gold/
carbon associations that at times extended far into the basin itself.
Where subsequently reworked, whether within or outside of the
preserved boundaries of the basin, these zones will have contributed
significantly to metallization in the conglomerate placers by normal
sedimentary processes. Recognition of this feature substantially eases
the problem of accounting for the total mass of WWR gold."
Whether the gold came from a hinterland rich in hydrothermal gold deposits as postulated or weathering from a source exhibiting no unusual gold concentrations in the form of chemically transported gold in solution or as colloids (that got caught by bacteria/bacterial/carbon mats) in the basin the ubiquitous thing that comes from the paper is that the morphology of the gold in the conglomerate at WWR is fine. The gold grains are small, on average 120 micrometres.
"From the inception of mining to 2002, the WWR has produced a
total of 49,332 metric tonnes (t) Au at an average recovery grade of ;8
g/t (Handley 2004). Individual reefs contain up to 1200 g/t. The gold
occurs in several distinct morphologies as discrete particles and
commonly forms some intergrowths on (and rarely in) pyrite; the
average size of gold particles is about 120 micrometers (Hallbauer and Barton
1987)."
There seem to often be larger grains of gold found in the ore (see image below) but not anywhere close to the size of nuggets. We are talking about visible grains of gold. I can't find any reference to nuggets being found within the conglomerates at WWR.
The coarser gold as I understand it was concentrated by biochemical processes and also fluvial action.
"Metallization was focused at several carbonaceous horizons along the north and northwestern margins of the WWR basin, depending on the availability of metal-rich aqueous fluids coincident with the stillstand of land surface degradation and the consequent proliferation of microbial mats. Biochemical processes supplemented low temperature geochemistry of the fluids in helping to concentrate a substantial portion of WWR gold in larger particles, which were transported further downslope and then subjected locally to fluvial processes."
On this basis if the Purdy conglomerates are similar to WWR normal drilling and assay techniques should give the answers.
Eshmun
(20min delay)