Letters A LODE-TYPE DEPOSIT?

I read with great interest your Research column (September issue) on Mother Lode-type deposits and environs. Eastfield Resources has a direct interest in the Pinchi Fault belt, and we believe that we are exploring a Motherlode-type deposit, though we are still in the early stages of exploration. While our understanding of the Pinchi Fault and its associate mineral occurrences remains somewhat juvenile at present, there are some interesting facts regarding our area that your readers might find enlightening. As you are aware, mercury occurrences proliferate along the Pinchi and, in our area, are exposed along the east side of Indata Lake, as well as in a mercury-laden hot spring at Tchentlo Lake. The mineralization at the Pinchi mine is localized along imbricated, east-dipping thrust faults. Similarly, the main zone gold mineralization at our Indata property is along moderately dipping structures whose dip is easterly. The main zone lies 3 km west of Indata Lake.

The Pinchi Fault is a complex structure whose breadth would appear to be measured in miles. We have also observed east-trending linears that appear to demark major vertical displacements in the generally north- to northwesterly- trending regional geology. We are speculating that these structures may be responsible for local block uplifts and, at our main zone, we see the exposure of a diorite- gabbro-amphibolite intrusive complex that may owe its surface presence to such uplift. An alternate thesis might be that we are dealing with distinct slabs of variably exposed portions of the Pinchi Fault through the process of thrust faulting.

I think one of the important points to note with regard to your article is the striking similarities in geology, structure and ore zone mineralization among the Bralorne-Pioneer mine, the Empire-Star in California and our own Indata Lake find. The Bralorne- Pioneer deposits have been considered by many geologists to represent a Motherlode-type deposit.

The Pinchi Fault has been explored by a number of major and junior companies over the decades, largely based on the same model we are pursuing. Placer gold deposits along the Pinchi were the motivation for belief in the model analogies. The low relief of the terrain and the attendant overburden cover were the inhibitors to discovery. The Indata is a classic example of a geochemical sampling discovery based on geologic modelling. There was no exposure of mineralization on our discovery zone, though hand trenching on a spectacular soil anomaly rapidly created the first exposure in the fall of 1987.

I apologize for the length of this letter, but it was refereshing to note that someone “back east” had awoken to the tremendous potential of this area. We are almost alone in exploring this region and hope that, with a little luck from Mother Nature, we will be exposing a major new district. G. L. Garratt, P. Geol., Vice-president, Eastfield Minerals Gold Centrefold Your map centrefold showing Canada’s top 100 gold projects in the September issue was spectacular. The North West Territories part was, unfortunately, misleading. The Tundra joint venture between Noranda Inc. and Getty Resources is 188 km due east of Indin Lake, about 2.3 cm farther than shown at the scale of your map. W. A. Padgham, Regional Manager, Geology Division, Indian and Northern Affairs Canada