The Jo Ann occurrence is situated in the Swannell Ranges (Omineca Mountains), approximately 19 kilometres north of Old Hogem and 59 kilometres northeast of Takla Landing.
The area is underlain by mesozonal plutonic rocks assigned to the Late Triassic to Early Cretaceous Hogem Intrusive Complex that have been emplaced into volcanic rocks of the Middle Triassic to Lower Jurassic Takla Group, east of the Pinchi fault zone. The plutonic rocks form an elongate batholith, extending from Chuchi Lake north to the Mesilinka River. The structural setting of the batholith and the intruded Takla Group is one of vertical tectonics associated with graben development (Bulletin 70).
Garnett (1978) mapped the area as being underlain by foliated migmatitic syenite of the Duckling Creek Syenite Complex, a Middle Jurassic phase of the Hogem Intrusive Complex. The only outcrop described by previous workers occurs on a small ridge northwest of the Lorraine occurrence (MINFILE 093N 002). Here, quartz deficient, intrusive rocks ranging in composition from syenite to diorite are locally potassium feldspar altered.
Numerous quartz veins, some hosting chalcopyrite and galena mineralization, are reported to cut the rusty, altered intrusions (Assessment Report 5649, page 3). In 1973, two short diamond drill holes collared to the west-northwest also intersected altered diorite carrying disseminated bornite. Grades of 0.02 per cent copper over 61.6 metres and 0.06 per cent copper over 46.9 metres were reported (Assessment Report 5993, page 3).
Work History
In 1972, a soil sampling program was conducted on the Jo Ann claims.
In 1973, an induced polarization survey was conducted along 20 line-kilometres and identified a zone of low susceptibility in the southern and western portions of the survey area and higher susceptibility within the northern and eastern portions, which was interpreted as resulting from low susceptibility syenite and higher susceptibility magnetite-rich dioritic rocks.
In 1974 and 1975, soil sampling and prospecting work was conducted on the Jo Ann claims.
In 1976 line-cutting work was completed to be used as a control grid for future geological work.
