The Treasure Mountain region is underlain by northwest striking, moderate to steeply southwest dipping volcanic and sedimentary rocks of the Lower-Middle Jurassic Dewdney Creek Formation (Ladner Group) and Lower-Upper Cretaceous Pasayten Group, intruded by numerous dikes and sills. The Dewdney Creek Formation comprises volcanic rocks and a minor amount of sediments and consists of tuff, breccia and agglomerate with interbedded argillite and conglomerate. The Dewdney Creek Formation is considerably altered; pyrite is commonly present and many outcrops are rusty. The Pasayten Group includes predominantly arkose, argillite and conglomerate. Locally, the two sequences are separated by a northwest striking, northeast-dipping fault, but in large part are conformable.

Mineral occurrences in the area are hosted in the Treasure Mountain fault and in and near subsidiary faults, and comprise one or more quartz-carbonate veins or stringers that branch and split and vary considerably in width and attitude (see Treasure Mountain, 092HSW016).

The Eureka occurrence is underlain by Dewdney Creek Formation volcanic breccia, conglomerate and argillite intruded by a large diorite sill 213 metres wide and 1.2 kilometres long. The Treasure Mountain fault crosses the area at 080 degrees with 30 to 65 degree dips to the south. The fault hosts a feldspar porphyry dike 1.5 metres wide. An adit explores the fault zone which consists of two faults separated by the feldspar porphyry dike, each to some extent containing mineralized quartz veins. The veins range from 1 to 30 centimetres in width, the hangingwall lode being the wider. The veins narrow towards the east. Mineralization consists of pyrite (more abundant here than in any other occurrences along the fault), galena, sphalerite and chalcopyrite, and possibly argentite and tetrahedrite.

The footwall mineralization occurs between the diorite sill and the feldspar porphyry dike. A sample across 25 centimetres of vein assayed 51.42 grams per tonne silver, 0.7 per cent lead and 25.3 per cent zinc (Minister of Mines Annual Report 1952, page A129). The hangingwall mineralization is between the feldspar porphyry dike and argillite, volcanic breccia and conglomerate. Quartz veins and stringers form a zone 0.9 metre wide. A sample across 25 centimetres assayed 305.09 grams per tonne silver, 5.7 per cent lead and 11.8 per cent zinc (Minister of Mines Annual Report 1952, page A130).

A parallel fault, 15 metres south of the Treasure Mountain fault, occurs in argillites. It is partly occupied by a quartz vein 1 to 25 centimetres wide, and strikes 075 degrees with 35 to 65 degree dips to the south. A sample across 15 centimetres assayed 89.12 grams per tonne silver, 2.3 per cent lead and 12.2 per cent zinc (Minister of Mines Annual Report 1952, page A130).

In 2005, drilling yielded intercepts of up to 309 grams per tonne silver, 3.54 per cent lead and 0.65 per cent zinc over 1.5 metres in hole HR05 located 40 metres south and 85 metres east of the Jensen adit (Ostensoe, E. (2008-07-30): Report of Property Review and Sampling Project – Treasure Mountain Property).

Work History

The area has been explored in conjunction with the nearby Treasure Mountain (MINFILE 092HSW016) mine and a completed property exploration history can be found there.

Minor production took place in 1927 with 21 tonnes being milled yielding 12.286 kilograms of silver, 3504 kilograms of zinc and 2739 kilograms of lead.

In 1988, a small rotary drilling program was performed on the occurrence.

In 2005, a program of reverse circulation drilling, comprising 5 holes with a total length of 316.5 metres, was completed in the vicinity of the Jensen workings to test the probable western extension of the main vein at about the elevation of the No. 3 Level.