The Curlew workings are hosted by the Lower Jurassic Rossland Group (Elise Formation) augite porphyry, known as the Rossland sill. The porphyry is dark green with phenocrysts of dark augite which are partly altered to hornblende. The Early Jurassic Rossland monzonite stock intrudes the Rossland Group rocks and the Curlew Crown Grant lies within the zone of thermal metamorphism.

The underground workings were initially centred on an ore vein from 15 to 25 centimetres wide. The ore is reported to be similar to that of the Blue Bird (082FSW145) which consists of quartz veins con- taining pyrite, sphalerite, galena, arsenopyrite, stibnite, chalco- pyrite, pyrrhotite and boulangerite. The ore is reported to have given assays from 10 to 17 grams per tonne gold and from 2400 to 2740 grams per tonne silver (Minister of Mines Annual Report 1896, page 31).

In 1908, 6 tonnes of ore were mined from a vein which produced 62 grams of gold and 3,608 grams of silver.