The Ato occurrence is situated in the Swannell Ranges (Omineca Mountains), approximately 20 kilometres northeast of Old Hogem and 40 kilometres west-northwest of Germansen Landing. Interest in the area began in 1962 when high-grade copper float was discovered in Rhondah Creek, a small north-flowing tributary to Wasi Creek.

The Rhondah Creek area straddles the contact between mesozonal plutonic rocks assigned to the Late Triassic to Early Cretaceous Hogem Intrusive Complex and volcanic and sedimentary rocks of the Middle Triassic-Lower Jurassic Takla Group. 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).

The Hogem Intrusive Complex is represented here by diorite, monzodiorite, monzonite and syenite, the latter belonging to the Middle Jurassic Duckling Creek Syenite Complex. The emplacement of this late magmatic alkalic phase appears to have resulted in a strong metasomatic overprint on the older intrusions. The syenite also appears to be spatially and genetically associated with sulphide mineralization in the area. Takla Group rocks include basic to intermediate volcanic flows with associated crystal and ash tuffs, limestone, dolomite and chert. These rocks are cut by dikes in the area of the contact and occur as xenoliths within the intrusive complex.

Porphyry copper mineralization is confined to a contact zone marked by coincident geochemical and magnetic anomalies, potassium feldspar-rich dikes and stringers and syenitic fracture fillings crosscutting both the intrusion and volcanic hostrocks near the headwaters of Rhondah Creek. The mineralization is in the form of fracture-hosted veinlets and associated disseminations of chalcopyrite, bornite, pyrite and magnetite. Pervasive potassium feldspathization is evident around the contact. A pyritic halo also occurs on the volcanic side of the contact, structurally above the copper mineralization.

During 1970 Tyee Lake Resources Limited acquired and staked mineral claims on Duckling Creek. These were known as the Duck, Rhonda and Duke Groups of claims. Exploration work in 1970 found copper-bearing float on the Rhonda claims. It was located in the vicinity of an intrusive contact and an associated soil geochemical anomaly. An induced polarization survey was conducted on the Rhonda Group in August 1970. This work resulted in the discovery of three anomalous zones. A follow-up examination of these sites found abundant disseminated pyrite mineralization and in one anomalous zone chalcopyrite and magnetite were located in float and outcrop. A stream geochemistry survey for copper was conducted in the same year. Four anomalous drainage basins were indicated in the survey. The most interesting is that of Rhondah Creek, where pyrite with copper mineralization and induced polarization anomalies have been found.

Five holes (P-70-1 to 5) drilled to test coincident geochemical/geophysical anomalies in the area of the original discovery intersected copper mineralization predominantly occurring in a feldspathized monzonite dike cutting altered Takla Group pyroxene porphyry. Pyrite, chalcopyrite and minor bornite were reported to be spatially associated with mafic alteration minerals (amphibole and biotite) and potassium feldspar-enriched zones. Pyrite and magnetite with rare chalcopyrite were also noted in the altered volcanics adjacent to the dike. The best results were from a 54.9 metre wide interval in hole P-70-1, which assayed 0.51% Cu (Assessment Report 21912, page 2). Subsequent percussion drilling and trenching in the area intersected only low-grade copper mineralization.

Measured geological reserves have been reported at 9 072 000 tonnes at 0.7 per cent Cu (1971) but could not be confirmed (Energy, Mines and Resources Mineral Bulletin MR 223).

An anomalous chargeability anomaly was outlined in the Rhonda area in 2005 Eastfield Resources Ltd which coincided with a mapped zone of potassium alteration and mineralized outcrops. Three drill holes were subsequently drilled in a fence over 400 metres to test this target. The holes all intersected broad zones of copper mineralization hosted within Takla volcanics that are intruded by numerous diorite dykes. The mineralization is associated with potassium feldspar flooding which is occasionally cut by later chalcopyrite-bearing massive magnetite veins. Drill hole 05-95 on the Rhonda intersected 94.9 metres averaging 0.24 per cent copper (Assessment Report 28186). The Rhonda zone is characterized by areas of pervasive potassic alteration, disseminations and veins of chalcopyrite +/- magnetite and local calc-silicate and propylitic alteration of both intermediate volcanics and diorite.

HISTORY

Kennco Explorations, (Western) Limited held the Dorel and Rhonda claim groups and during 1961-1963 carried out geological, geochemical, and geophysical surveys.

Tyee Lake Resources Ltd., incorporated in 1969, acquired the Rondah, Duck, and Duke claim groups by staking. Work during 1970 included geological mapping, an induced polarization survey over 10 line-miles, a geochemical soil, silt, and. rock chip survey, trenchirig, and 914 metres of diamond drilling in 5 holes to explore coincident anomalies; the most significant mineralization reported was a 54.86 metre section assaying 0.5 per cent copper and 0.02 per cent molybdenite.

In June 1971 a joint exploration agreement was reached with Cominco Ltd. and Marubeni-Iida (Canada) Limited. Work during the year included geophysical and. geochemical surveys, trenching, and percussion drilling in 10 holes totalling 609.6 metres. This work indicated a zone 30.5 metres wide and at least 122 metres long grading about 0.4 per cent copper. Cominco and Marubeni continued the exploration work in 1972, including induced potential and ground magnetometer surveys over 8 line-miles, trenching, and 359.6 metres of percussion drilling in 8 holes on the Duck claims. No further work was carried out and Tyee Lake Resources allowed the claims to lapse in 1976.

The 2005 exploration program by Eastfield Resources Ltd covered several target areas and led to IP geophysical survey tests in three areas, the Steelhead, North Dome and Rhonda. An anomalous chargeability anomaly was outlined in the Rhonda area which coincided with a mapped zone of potassium alteration and mineralized outcrops. Three drill holes were subsequently drilled in a fence to test this target.

See Lorraine (093N 002) for a general discussion of the history which includes the Rhonda area.