Tollu Project – JORC Resource and Conceptual Exploration Target Geology
Multiple field visits were completed by BM Geological Services (BMGS) to gather additional data for the purpose of constructing the Conceptual Exploration Target (the Target). Outcropping vein geometries were mapped and measured in detail with emphasis placed on paragenesis of mineralisation.
Field observations identified that phases of mineralised quartz veining are located within low stress, dilatational jogs caused by the reactivation of a regional scale reverse fault (Tollu Fault) (Table 1). The Tollu Fault has been interpreted as a deep-seated transform structure of the NW-SE striking Tjuni Purlka Tectonic Zone situated to the north (Figure 1).
An early, uniform, phase of veining appears to be related to an initial structural phase (probably reverse faulting) and is characterised by unmineralised, banded, ferruginous quartz (Table 1). This initial veining is interpreted to represent the primary structural architecture. Subsequent reactivation of this structure has created dilatational jog positions which have been exploited by mineralised fluids. Several quartz vein phases have intruded during this reactivation and at least two of these phases appear to be mineralised (Table 1). The mineralised vein phases are lenticular in shape which limits their strike width and length.
|Structural Phase||Veining Type||Mineralisation||Veining size|
|Reverse Fault||Banded, ferruginous quartz||Unmineralised||Uniformed vein widths outcropping for several kms|
|Reverse Fault – Reactivation of initial fault phase creating low pressure dilatational jogs||Very coarse grained, interstitial quartz crystals (‘Hounds Tooth”)||Unmineralised||Small scale lenses over tens of meters|
|Fine grained buck quartz + malachite||Low grade Cu||Small, lenticular; 0.5-2m wide and up to 20m long at surface|
|Faulted quartz + clay + malachite||High grade Cu||Small, lenticular; 0.5-2m wide and up to 20m long at surface|
|Massive buck quartz||Unmineralised||Large quartz blows up to 100m long and 30m wide|
Table 1 – Tollu Vein Paragenesis identified during the March 2014 field mapping programme
The dilatational jog positions occur randomly along the strike extent of the Eastern and Main Reef Prospects but generally at intervals of 100-300m. This observation was used as a parameter to assign tonnes and grade to interpreted mineralised positions under cover.
The mineralisation comprises sub-economic to ore-grade copper mineralisation, occasionally containing elevated concentrations of cobalt and minor concentrates of tungsten and silver. The copper mineralogy is chalcopyrite and bornite at depth and malachite within the regolith.
Figure 1 – District scale structural interpretation illustrating the Tollu Fault’s relationship with the Tjuni Purlka Tectonic Zone
(After Smalley 2014)