LETTERS TO THE EDITOR — Pluton search

Regarding Eva Schandl’s letter “New light on Sudbury-type rocks” (T.N.M., Aug. 3/92), I like the idea of calling upon “. . . the presence of mineralized source rocks at depth.” In the Nelson, B.C., area, I call them “sub-surface plutons.” According to a recent survey covering the area, LnCo/LnNi ratios in the range of 0.8-1.0 account for 25 out of 27 gold values at or above 100 ppb.

In “Genesis of Archean Volcanic Hosted Gold Deposits,” OGS Miscellaneous Paper 97, pp. 86-87, Co and Ni values are given for Balmertown and Cochenour twps. and for Dickenson’s White mine. Their ratios range from 0.40 to 0.93 with a correlation coefficient of 0.74. This is significant at the 99% level. This means that these ratios can be used for contouring and, I hope, will help identify “sub-surface plutons” leading to more gold discoveries. George Addie

Addie Consultants Ltd.

Nelson, B.C.