St George defines large VMS prospect at East Laverton
VMS potential at the East Laverton Property was highlighted through the results of the 2012 reconnaissance drilling completed by BHP Billiton Nickel West as part of the previous Project Dragon farm-in arrangement.
That drilling intersected thick metal‐rich and sulphide‐rich sediments with elevated levels of zinc and copper mineralisation. The sulphide units intersected by the drilling were up to 90 metres thick with mineralisation grading up to 4460 ppm zinc and 1400ppm copper.
The presence of both komatiite hosted nickel sulphide mineralisation and VMS hosted base metal at East Laverton is consistent with the genetic relationship that exists between these styles of mineralisation.
Volcanic massive sulphide lenses are an important source of crustal sulphur which is required for the formation of nickel sulphide deposits.
The relationship between nickel sulphide and VMS mineralisation means that preserved VMS deposits would typically be hosted by rocks away from the main ultramafic belt.
St George Mining Executive Chairman, John Prineas noted:
“This is an exciting development which backs up our great confidence in the potential for a range of metal discoveries at East Laverton in addition to the proven nickel prospectivity there.
“We are really looking forward to returning there in October for the next round of drilling as we continue to define the great exploration opportunity we have at East Laverton.”
Favourable prospect geochemistry
A review of the geology and geochemistry suggest that a marginal section of a larger VMS system may have been intersected.
The modelled electromagnetic conductor Dragon 3 is adjacent to the banded sulphide mineralisation intersected, and could represent a more central part of the VMS system, where there is a greater likelihood of more massive style mineralisation and higher base metal grades.
This area remains to be tested and is a priority drill target for the Phase 2 drilling program, scheduled for October.
VMS deposits have a stacked and zoned alteration profile with a predictable geochemical zonation which assists in understanding where a single drill intersection is situated within the wider mineral system.
The geochemical and alteration profile of the intersection is consistent with a distal part of a VMS mineral system, with elevated levels of sulphur, magnesium, potassium, barium, and lead in comparison to the country rocks.
This is a typical geochemical profile for VMS mineralisation; elevated potassium is related to sericite alteration, and elevated magnesium is related to peripheral magnesium‐rich chlorite alteration formed by interaction with sea‐water.
The more central parts of the mineral system, which are preserved from extensive sea water interaction, are iron‐chlorite dominant.
The elevated zinc and copper in the sediments are formed in a dynamic exhalative environment associated with volcanic vents, again consistent with distal VMS‐style mineralisation.