The Heidi (Greenfield) occurrence is located a short distance north of Heidi Lake and approximately 7.2 kilometres south-southeast of Mount Milligan.
The area is underlain by the Upper Triassic Takla Group consisting of north-northwest–trending volcanic rocks of the Witch Lake Formation and minor sedimentary rocks of the Rainbow Creek Formation. The Witch Lake rocks are intruded by coeval Takla Group and post-Takla Group intrusions related to the informally named Lower Jurassic Mount Milligan Intrusive Complex centred around Mount Milligan to the north.
Locally, as defined by diamond drilling, a monzonite porphyry stock (Heidi stock), generally comprising dikes up to 10 metres wide, intrudes andesitic rocks and hosts low-grade porphyry copper-gold mineralization. Alteration patterns include a mix of early-stage potassic and sodic-calcic (albite-actinolite-chlorite) assemblages overprinted by propylitic and late-stage quartz-sericite-pyrite-carbonate assemblages. Early to transitional vein types include pyrrhotite-bearing polymetallic veins that can be massive and disseminated pyrrhotite appears to be part of the sodic-calcic alteration assemblage.
In 2018 and 2019, drilling on the Heidi zone yielded intercepts including 0.206 gram per tonne gold and 0.132 per cent copper over 20.00 metres (568.00 to 588.00 metres down hole) in hole 18-1104, 0.074 gram per tonne gold and 0.205 per cent copper over 33.60 metres (17.00 to 50.60 metres down hole) in hole 18-1106 and 0.048 gram per tonne gold with 0.154 per cent copper over 83.73 metres (24.00 to 107.73 metres down hole) in hole 19-1179 (Fitzgerald, J., Jago, C.P. [2019-12-31]: Technical Report on the Mount Milligan Mine, North-Central British Columbia).
Work History
The area has been explored in conjunction with the nearby Mount Milligan (MINFILE 093N 194) occurrence and a complete regional exploration history can be found there.
In 2018 and 2019, Thompson Creek Metals Company Inc. completed programs of ground and airborne geophysical surveys and diamond drilling on the area as part of the Mount Milligan property.
