More bonanza grades in Copperstone’s D zone

Staying true to its name, American Bonanza Gold Mining (BZA-V) has pulled more high grades from its Copperstone property in Arizona.

Hole 4, collared at the southern end of the so-called D zone, yielded 15.3 grams per tonne over 4.4 metres (starting at 17 metres downhole) and 22.9 grams over 9.8 metres (from 45 metres). The latter interval contains a subzone that ran 43 grams over 3.7 metres.

The results are similar to those of hole 3, which returned 41 grams over 12.2 metres (from 29.3 metres). That hole also contained several higher-grading subintervals, of which the richest carried 107 grams over 1.8 metres.

A follow-up hole, 5, was stopped short of the main structure; however, before its termination, it pulled up 2.2 metres (from 27 metres) running 5.7 grams and 4 metres (from 31.7 metres) running 3.4 grams. The hole will be extended.

(Holes 1 and 2 targeted the western margin of the zone, and only the latter returned any significant results. Starting 14 metres downhole, it averaged 2.1 grams over 5 metres and, from 24 metres, 6.5 grams over 2.7 metres.)

The D zone varies from 4.6 to 6.1 metres in true-thickness and lies 183-198 metres below surface. Gold mineralization is restricted to fault zones in a package of Triassic-aged sedimentary and Jurassic-aged quartz-latite volcanic rocks. The structures strike to the northwest and dip at shallow to moderate angles.

Associated alteration minerals include hematite, magnetite, chlorite and silica. Some gold has been picked up in the wallrocks, though not in significant abundance.

Drilling along the strike and downdip projections of the faults continues.

The current campaign, which will entail about 2,700 metres, is being carried out from a decline that was extended earlier this year to intersect an old surface hole that pulled 3 metres of D-zone mineralization averaging 182 grams. The ramp starts on the northern floor of the old Copperstone pit (T.N.M., Nov. 12/03).

The D zone is one of two, the other being C, that host a combined 1.9 million tonnes of indicated and inferred resources averaging 11.7 grams gold. The D zone alone hosts 826,260 tonnes grading a cut 14.7 grams, using a cap of 161 grams.

Uncut, the zones average 19.9 grams.

The estimates were calculated in 1999 by MRDI Canada and are based on the results of 71 holes. Of those, 15 were drilled by American Bonanza’s predecessor, Asia Minerals; the rest, by previous owners.