The Early Jurassic Tulameen Ultramafic Complex is an elongate northwest-trending body, 17 kilometres long and 2.5 to 6.5 kilometres wide. The hostrocks to the intrusion are andesitic metavolcanics and metasediments of the Upper Triassic Nicola Group, locally metamorphosed from greenschist to amphibolite grade. To the north and northwest, granodiorite of the Late Jurassic to Early Cretaceous Eagle Plutonic Complex truncates the northern margin.
The dunite core of the complex occupies the slopes of Olivine and Grasshopper mountains and the intervening valley of the Tulameen River. The core is roughly oval in shape and covers an area of about six square kilometres. Mapping by Findlay (1963), outlined areas with 20 to 80 per cent serpentinization. The degree of serpentinization decreases, in general, from east to west. Essentially unaltered olivine is required for industrial purposes.
Detailed mapping and sampling of the least altered zone of the core (less than 20 per cent serpentinized) was done in 1986 by G.V. White of the Geological Survey Branch. One hundred and ten 0.5-kilogram grab samples and three 100-kilogram bulk samples were taken. Seventy-four of the grab samples were tested for loss on ignition, 19 of which were below two per cent. The 19 samples outlined three significant areas of "fresh" dunite on the lower slopes of Grasshopper Mountain that showed initial potential for raw olivine. All the samples taken from Olivine Mountain had loss on ignition values in excess of 2 per cent. The three zones are described by White (Fieldwork, 1987) as follows:
"Three zones with loss-on-ignition less than 2 per
cent have been identified north of the Tulameen River
on the southwest slopes of Grasshopper Mountain. The
northern zone, approximately 100 metres long by 75
metres wide, is open to the east. A second, central
zone is approximately 50 metres long by 40 metres wide
and open to the west. The third, irregular zone, cut
by the Tulameen River road, is approximately 100 metres
long by 65 metres (maximum) wide."
Sampling was not carried out on the southeastern slopes of Grasshopper Mountain or the northeastern slopes of Olivine Mountain due to the difficulty of access. These areas are within the less than 20 per cent serpentinized zone as outlined by Findlay (1963) and therefore have the potential for fresh olivine. The bulk samples taken from the zone along the road were shipped to CANMET laboratories in Ottawa for further testing. The results are described below.
In 1986, a 20-kilogram sample was tested to determine if it would be suitable for foundry sand applications. The testing considered several properties including crushing and screening characteristics, mouldability, clay and water requirements, wet and dry compressibility and permeability. The Grasshopper Mountain olivine sand performed well, or adequately, in all categories in the initial testing. Due to the favourable performance, a second, larger bulk sample was shipped to CANMET for full scale testing as foundry sand.
In 1987, a 454-kilogram bulk sample taken along the Tulameen River road, 113 metres west of the mouth of Britton Creek, was shipped to CANMET for detailed foundry sand testing. The examination included optimum crushing method and grain characteristics. Also examined was the greensand preparation including clay and water requirements, compactability, density, mold hardness and mouldability. Further, the casting performance was assessed for burn-on, scabbing, surface finish and mold penetration. The performance of the sand with repeated use was tested by five sequential castings and the sand was examined for moisture content, clay demand, grain sizing and attrition as well as acid resistance and loss on ignition.
The olivine test sand from Grasshopper Mountain performed well against an industry standard sand, IMC Olivine 50, from the United States. Most results were equivalent and little variation occurred between tests. This indicates that the olivine from Grasshopper Mountain could perform well against sands already available on the market.
Subsequent work was conducted by Dia Met Minerals Ltd., along and above the Tulameen River road, about 400 metres southwest of the mouth of Britton Creek. Here, the dunite is variably serpentinized, with both fibrous and asbestiform varieties of serpentine replacing 10 to 90 per cent olivine along grain boundaries and internally. Talc replaces 2 to 5 per cent of the olivine, and minor carbonate alteration is also noted. Loss on ignition for most of the olivine ranged from 2.0 to 4.0 per cent. Beneficiation tests on 23 dunite samples from drill core indicated no sample with greater than 3.5 per cent ignition loss could be reduced to less than 2 per cent ignition loss by grinding and gravity separation (Assessment Report 19480).
The company drilled two holes in 1988, and conducted mapping and surface sampling over a 300 by 200 metre area in 1989.