Great Basin pursues Midas-style veins — Veining, mineralogy seen as analogous to Ken Snyder

A drilling program at the Ivanhoe property in Nevada is aimed at following up the discovery of Midas-style veining in the Valmy formation, reports Great Basin Gold (GBDG-V).

The company discovered the veining earlier this year while exploring for a Carlin-type deposit, that is, finely disseminated gold and arsenic-sulphur minerals hosted in domed and fractured carbonate rocks.

Advances in the understanding of the Carlin-type geologic model have led to the recognition of deep mesothermal roots in mineralizing systems. The implication is that near-surface, lower-grade deposits can be viewed as precious metal leakage anomalies that provide evidence for larger, high-grade gold systems formed in favorable hosts at depth.

In the case of Ivanhoe, relatively low-grade gold mineralization in Tertiary-aged volcanics and upper plate Valmy siliclastic rocks are thought to conceal a large, high-grade gold system in lower-plate carbonate rocks at depth.

Great Basin’s program of exploring for deep gold deposits is based on detailed geological mapping and sampling, as well as closely spaced shallow drill holes. These techniques have focused on identifying ore-controlling feeder structures, high-grade zones of fault intersections, and orientations of high-grade shoots. The resulting targets occur where high-grade shoots are projected to intersect favorable host rocks at depth.

In early 1998, Great Basin completed a shallow drilling program in the Hollister mine area of the Ivanhoe property. The program was designed to map mineralized faults. A fence of six vertical core holes was put down on roughly 25-ft. centres. The first hole intersected banded quartz veins with minor amounts of electrum and naumannite (silver- and gold-bearing minerals). The third hit strong naumannite-aguilarite in quartz kaolinite veins that assayed up to 11 oz. gold and 103 oz. silver per ton over 4.6 ft.

The veining style and mineralogy were recognized to be analogous to the Ken Snyder mine, currently being developed by Franco-Nevada Mining (FN-T) and Euro-Nevada Mining (EN-T). Great Basin therefore shifted its exploration focus to the Midas-style quartz-kaolinite veining in the Hollister area.

Extensive drilling and underground development at Ken Snyder has demonstrated a strong stratigraphic control to veining in the area, with felsic volcanics providing the better host to thicker vein zones. Similarly, the quartzite packages in the Valmy formation appear to be superior hosts for gold veining at Hollister.

The thickest and highest-grade section at the Ken Snyder deposit seems to be associated with the intersection of northwest and north-south faulting.

Great Basin will target similar structures that represent major fault intersections in the Valmy quartzite package.

Currently, a 23-hole drilling program is focusing on the strike continuity in the quartzitic beds of the Valmy formation, southeast of the 6-hole discovery area.

The company plans to investigate one other target: intrusive-hosted and intrusive/upper plate contact-hosted gold zones associated with the Hatter granodiorite stock. These are situated just east of the Hollister area. One hole from the 23-hole program will test the area just northwest of the Hatter stock; the hole will be drilled into the silty carbonate rocks of the lower-plate Popovich formation.