The Koopa Bowl occurrence is located about 5.2 kilometres south-southwest of Bowser Lake approximately 51 kilometres north of the community of Stewart.
The Koopa Bowl area is underlain by rock of the Upper Hazelton Group, referred to as the Iskut River Formation. The formation includes bimodal volcanics, as well as porphyritic intrusions and debris flows. The Iskut River Formation is capped by black carbonaceous pyritic mudstone interbedded with a light and dark banded tuffaceous siltstone, which are distinct in the region and referred to as the Quock Member (formerly known as the “pyjama beds”). Locally, the base of the Quock Member includes well sorted sandstone and conglomerate beds.
Mineralization at the Koopa Bowl prospect occurs over an area of 500 by 700 metres and is hosted at the contact between the Iskut River volcanics and the Quock Member mudstones, with abundant 10-centimetre-wide quartz veins strongly mineralized with pyrite, pyrrhotite, stibnite, galena, and sphalerite. Four samples contain greater than 1 gram per tonne gold, with values ranging from 1.35 to 5.28 grams per tonne gold. An additional five samples have greater than 100 grams per tonne silver, with the best sample assaying 1460 grams per tonne silver, 0.965 per cent copper, 8.95 per cent lead, and 25.4 per cent zinc (sample B048463, Assessment Report 37443). Samples that are enriched in gold typically show an association with pyrite, whereas silver-rich samples are typically associated with galena, sphalerite, and stibnite.
In 2019, Pretium Exploration Inc. completed three drillholes on the Koopa property, for a total of 1488 metres. The collars were drilled from two drill pads, located at 1560 and 1650 metres elevation in a glacial cirque at the base of a receding glacier. The drillholes were planned to target quartz plus pyrite veins exposed on surface and to test the potential for an intrusion-related gold system hosted in the Iskut River Formation stratigraphy. Drilling encountered two generations of quartz veins, with low grade gold associated with quartz plus pyrite veins, and silver plus lead plus zinc mineralization associated with quartz plus stibnite plus sphalerite veins. In drillhole BR-037, a 1.0 metre interval assayed 0.05 gram per tonne gold, 109.0 grams per tonne silver, 4.75 per cent lead and 0.56 per cent zinc. In drillhole BR-039, a 3.82 metre interval assayed 1.25 grams per tonne gold and 42.27 grams per tonne silver (Assessment Report 38606).
Historically, only limited work has been conducted on the Koopa property; B.K. Bowen collected 58 silt samples and 13 rock samples in 2005, and one mineralized float sample from the northeastern part of the property assayed 5.89 grams per tonne gold and 64.8 grams per tonne silver. In 2010, a hyperspectral survey was carried out on the claims and an anomaly (tentatively classified as buddingtonite) was identified approximately 3 kilometres north of the well mineralized float sample. In 2017, 343 grab samples were collected from the Koopa property and surrounding areas. A 500 by 700 metre topographic bowl was identified in the northwestern corner of Koopa which hosted mineralized quartz veins at the contact between the Iskut River volcanics and the Quock Member mudstones. In 2018, two drillholes were completed on the Koopa property, totalling 287 metres. Both holes were drilled off the same pad, at 1560 metres elevation in a cirque at the base of a receding glacier, in order to test the Iskut River Formation stratigraphy in the area, which regionally hosts volcanogenic massive sulphide (VMS)-style mineralization. The drilling did not encounter elevated precious or base metals, and the alteration appeared to be distal from a possible VMS producing hydrothermal cell. Indicator elements, including arsenic and antimony, were moderately elevated, which suggested there may be a mineralization system buried on the property.
Prior to 2014, Pretium Resources put together a very large block of contiguous claims called the Bowser property, stretching from Brucejack Lake to Bowser Lake and farther to the south and southwest, to Summit and Long lakes. The Bowser Regional Project area, approximately 20 kilometres southeast of the Valley of the Kings deposit, comprises approximately 800 square kilometres.
In 2014, on behalf of Pretium Exploration on their Bowser property, an 1885 line kilometre magnetic and radiometric survey was flown at 400 metre line spacing. Due to inclement weather, only 350 line kilometres of Time Domain Electromagnetics were flown (Assessment Report 36790). In 2015, Pretium Exploration expanded the magnetometer and radiometric survey area to the east and south, as well as infilling specific block areas to 200 metre line spacing. A total of 1139 kilometres of magnetics and radiometrics were completed. In 2015, the proposed 2014 Time Domain Electromagnetics survey blocks were also completed, and the Time Domain Electromagnetics survey grid was extended to match the area covered by the 2015 magnetometer and radiometric grids, totalling 3402 Time Domain Electromagnetics line kilometres flown that year. Follow-up work was to focus on areas where the resistivity and conductivity indicate alteration, and the conductive anomalies might indicate massive sulphide bodies.
In 2016, Pretium Exploration initiated a 4 kilometre Magnetotelluric line starting in the Canoe Glacier valley, crossing over the toe of the Knipple Glacier and continuing on to Scott Creek. A Direct Current Induced Polarization survey was also completed, focussing on the Salmon River Quock Member sediments and the underlying volcanics at the Kirkham, Pipe Dream, Knipple Lake, and Cone zones. Ten Direct Current Induced Polarization lines, covering 23.5 kilometres with 19 Magnetotelluric sites, as well as 26 Magnetotelluric stations covering the Bowser Valley were completed. In order to expand the structural and lithological interpretation at KL Gossan and KL East zones, where outcrop exposure was minimal, 24 more Magnetotelluric sites were surveyed. The results of this 2016 work included the identification of 55 zones of interest related to resolved anomalies over Cone Zone (5), Kirkham (18), Pipe Dream (21), regional Magnetotelluric Transect line (5), and Bowser infill Magnetotelluric area (6) (see Assessment Report 36790 for further information).
In 2016, Precision GeoSurveys Inc., on behalf of Pretium Exploration, completed a 1400 line kilometre airborne magnetic and radiometric survey on the Bowser property. The survey covered the southern end of the Bowser property, as an irregular 24.7 by 23 kilometre block, with 200 metre line spacing, flown north-south, and 2 kilometre tie lines. The purpose of the survey was to complete the magnetometer and radiometrics coverage over the entire Bowser property claim area, as the northern extents of the property had previously been flown in 2014 and 2015. See Assessment Report 36793, Appendix III for Precision's, "Airborne Geophysical Survey Report", including 2014-2016 magnetic and radiometric maps.
In 2017, Pretium Exploration conducted grassroots prospecting, sampling, and mapping on their Bowser property, mostly southwest and south of Bowser Lake. They collected 2901 rock and 429 silt samples (Assessment Reports 37435, 37443). It was during this program that the Koopa Bowl prospect was discovered. Several new MINFILE occurrence are documented and a number previously documented occurrences were visited by Pretium.
In 2018, beyond the Brucejack mine area (104B 193), Pretium continued to evaluate their surrounding 1250 square kilometres of mineral claims. From July to October, 31 diamond-drill holes totalling 7725.1 metres were completed on the Bowser property; 10 holes tested the Lilliane (104A 112), 2 holes tested the Moonlight (104A 005), 9 holes tested the Bluffy (104B 075), 1 hole tested the Virginia K (104A 118), 3 holes tested the Outlaw (located 1.3 kilometres north of Moonlight Glacier 1 (104A 120), 4 holes tested the Haimila (104A 226), and 2 holes tested the Ridgeback (located 1.9 kilometres west of Koopa Bowl (104A 233). The exploration targets were widespread and drillholes targeted epithermal, porphyry copper, shear zone-hosted gold, and volcanogenic massive sulphide (VMS) style mineralization. The company also carried out mapping and prospecting (Assessment Report 38235).
As of September 2019, two drills were testing the high-priority A6 zone volcanogenic massive sulphide (VMS) target located 14 kilometres northeast of Brucejack mine; a third drill targeted a VMS system at the Canoe zone (104B 732, 734) located 15 kilometres west-southwest of Sharktooth; and a fourth drill targeted an intrusion-related gold system at the Koopa zone (104A 222, 229, 233) located 10 kilometres south of the Sharktooth. Drilling earlier in the summer also focussed on the Tuck zone (104B 730) located 22 kilometres west of Sharktooth and Liliane zone (104A 112) located 17 kilometres south of Sharktooth, both epithermal gold system targets.
To date (2019), approximately 26,103.1 metres have been drilled in 81 holes. To facilitate exploration work, the Bowser property has been divided into zones and the drilling took place in seven of these zones: A6 Anomaly, Canoe, Koopa, Tuck, Haimila, Kirkham, and Lillianne (Assessment Report 39085).
See Betty (104A 008), located 28 kilometres south of Sharktooth, for details of relevant work done on Pretium's grassroots project on their Bowser property, including significant property-wide geophysical surveys completed prior to to 2017. Refer also to West (104B 193), located 23 kilometres west of Sharktooth, for details of related mineralization and a common work history relating to the Brucejack project of Pretium Resources.
