The Dorothy occurrence is situated in the Duckling Creek area of the Swannell Ranges (Omineca Mountains), approximately 15 kilometres northeast of Old Hogem and 41 kilometres west-northwest of Germansen Landing. The area first became of interest in the late 1940s when copper-bearing float was discovered on the slopes east of Duckling Creek.
The area is underlain by mesozonal plutonic rocks assigned to the Late Triassic to Early Cretaceous Hogem Intrusive Complex which 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).
Late Triassic to Early Jurassic rocks of the Hogem granodiorite and basic suite dominate in the area of the Dorothy occurrence. The intrusions vary compositionally from diorite to quartz diorite, although pyroxenite outcrops are quite widespread. These rocks intrude volcanics assigned to the Takla Group to the east and south. These rocks consist of dark green tuff and volcanic breccia of basaltic to andesitic composition, interbedded with flow rocks and commonly cut by pyroxenite and feldspar porphyry dikes.
The occurrence is exposed at an elevation of approximately 1350 metres in a series of east-west trenches located uphill from the mineralized float. The host microdiorite is a finely crystalline dark grey to green, somewhat foliated unit characterized by weak chlorite and epidote alteration and abundant accessory magnetite. It appears to have been hornfelsed as a result of later intrusive activity, resulting in a fine biotitic foliation. Gneissosity striking 080 to 090 degrees and dipping steeply south has also been noted in a few outcrops. Finely disseminated pyrite and chalcopyrite locally comprise over 10 per cent of the rock. The zone extends 500 metres north and 200 metres east-west.
A 91-metre wide quartz plagioclase dike also strikes northerly across the area. The dike varies from aplitic near its margins to medium grained towards the centre and reportedly hosts minor disseminated pyrite. Narrow stringers of pegmatite cut both the dike and diorite in outcrops to the north.
Dioritic talus and bedrock exposed in early trenches reportedly hosted irregularly disseminated grains, blebs and small stringers of chalcopyrite and pyrite with minor bornite, covellite, pyrrhotite, molybdenite, sphalerite and galena. The chalcopyrite reportedly occurred sparsely in the more pyritic, quartz-rich diorite. Drilling determined that the copper mineralization occurred in irregularly silicified areas within the diorite, and that they had little continuity in either strike or dip. The average grade of a few drill sections as much as 15 metres long reportedly varied from 0.5 to 1.0 per cent copper (Geology, Exploration and Mining in British Columbia 1971, page 215).
The nearby Elizabeth showing (093N 074) was examined by Lysander Minerals Corp. in 1999 as part of its Jajay property. Eastfield Resources Ltd. optioned the Jajay property in 2001. See Lorraine (093N 002) for details.
HISTORY
The Dorothy group of 18 claims was staked in 1948 for Zennex, Limited, and transferred to Northwestern Explorations, Limited, which was incorporated in 1949; the claims were staked to cover three copper-bearing talus slides that occur at intervals over a distance of 335 metres. Trenching was reported in 1948, and diamond drilling in 4 holes totalling 439 metres in 1949. During 1951 a biogeochemical survey using tree samples was carried out to test this method. The company name was changed in 1959 to Kenuco Explorations, (Western) Limited. Geological, geophysical, and geochemical surveys were carried out during 1961 and 1962. During 1972, Kennco carried out geological mapping and. trenching. In 1989, Kennecott Canada Inc. began a reassessment of the gold-copper potential of the Lorraine and Dorothy properties.
In 1991, work consisted of road construction (from the Dorothy-Duckling Creek access road to the Elizabeth Breccia area), test pitting, rock sampling, IP surveys and The diamond drilling of 6 NQ holes for a total of 961.6 metres. The first 3 holes were drilled at the Dorothy showing in the vicinity of Northwestern’s 1949 drillholes, the remaining 3 holes were drilled along the Dorothy Duckling Creek road south of Dorel Creek. The most significant intersection was in hole D91-1 which averaged 0.34 per cent copper and 0.12 grams per tonne gold over 12 1 metres (Assessment Report 28186).
In 1996 Lysander optioned the Dorothy and Steelhead properties and staked the Pal claims.
Lysander continued drilling in 1997 with an 8-hole (1146.3 metres) program on its Lorraine Jajay property. Four holes were drilled in the Dorothy showing, 3 holes in the Bishop zone and 1 hole in the Ato area (Bobinette claim).
Prospecting and mapping by Eastfield occurred in the Dorothy area in 2004 and 2005. Relogging of holes in 2005 (91-02,03; 97-01,02,03) demonstrated a wide variety of mineralization and alteration not clearly expressed in the surface showings. Surface showings are generally pyrite dominant fine grained diorite with variable fracture and disseminated chalcopyrite. This rock is typically moderately to strongly sericite altered with varying intensity of alteration and mineralization.
In 2005 Teck Cominco conducted an airborne magnetic and radiometric survey over it large Lorraine-Jajay property, including the Dorothy area. A mag high feature is located in the northeastern area of the survey (Rhonda – Dorothy area) and is due in part to the Dorothy and Rhonda diorites.
