94 REPORT OF THE MINISTER OF MINES, 1929.

MINERALIZATION RELATIVE TO Minrne MEtTrHops.

Should the complex sulphide ore-bodies of the Taku region ultimately prove to be of com-
mercial extent and grade, their structure and mode of mineral occurrence suggests a method of
mining that might be advantageously employed to meet the constantly changing economic aspect
of the metal market. The characteristic central segregation of chalcopyrite that apparently
occurs over good widths and appreciable lengths in the Tulsequah Chief and Manville ore-shoots
may permit the mining and treating of a good-grade copper-gold ore when the market price for
copper is advantageous and that for zine and silver is not. The ore containing mainly a zine
content, occurring lateral to the chalcopyrite segregations, could be attacked when the market
price for zinc became advantageous.

It would seem that on both the Tulsequah Chief and the Manville the opportunity may
prevail to selectively mine an ore containing from 3 to 9 per cent. copper, 0.2 oz. gold to the ton,
and 2 oz. silver to the ton, with a reduced content of zine. In considering this means of meeting
the metal-market situation, however, there are many intricate factors to be earefully calculated.
In mining selectively for the copper-gold contents a dilution with zine could not be avoided at
any time. The economic point of zine dilution relative to mining widths and costs, the bearing
of this factor on milling practice and costs, the comparative costs of mining methods relative to
tonnage production and grade of ore mined, the factor of interest, are all interlocking questions
involved in the calculation. The mode of occurrence of the mineralization in the Tulsequah
Chief and Mamnwille ore-bodies, however, suggests the possible economy of such a selective type
of mining. The scheme is mentioned as being worthy of consideration on account of its bearing
on the ultimate possible profitable operation of the Taku River complex sulphide ore-bodies,
should they prove to be of economic extent.

MINERAL PROPERTIES.

The important properties in the area are: The Tulsequah Chief, Manville, Big Bull Exten-
‘sion, Potlatch (Sparling), Banker (Hill), and Whitewater.

TULSEQUAH CHIEF.

(See Annual Reports for 1923 and 1928.) This property comprises eighteen surveyed claims.
It is situated on the eastern bank of the Tulsequah river, about 8% miles north-easterly from
its confluence with the Taku. It was originally staked by A. W. Kirkham, of Juneau, Alaska,
and bonded to the Alaska Juneau Gold Mining Company in 1923. This company relinquished
its option in the same year. In 1928 the property was bonded to Dan J. Williams, W. A. Eaton,
of Juneau, and associates. In the spring of 1929 this syndicate bonded the property to the
United Eastern Mining Company, of Los Angeles, which has been developing it from that date.

A warehouse and log cabin are located at the landing-point on the Tulsequah River bank.
The operating camp is situated on a bench area at altitude 1,050 feet. A crew of thirty to forty
men has been continuously employed during the season. The workings are at 1,500 and 1,700
feet altitude. The property is efficiently equipped with a compressor, machine-drills, blowers,
and steel-sharpening outfit. A skidway haulage system in two sections, powered by 8- and
10-horse-power gasoline-engines, operates from the warehouse on the viver-bank to the camp,
and from thence to the portal of the lower tunnel. Operations are being conducted under the
personal supervision of J. B. Stapler, general superintendent and manager.

Geologic Featwres—The ore occurrence consists of two replacement shear-zones in altered
and pyritized rhyolite, in a formation of dense-textured andesitic fragmentaries and flows. No.
1 zone strikes N. 45° EB. and No. 2 zone N. 20° BE. Both zones show a tendency to an erratic, but
generally steep, westerly dip. The two ore-zones are separated by a dacite dyke 8 feet wide,
striking parallel to and in contact with No. 2 zone. The rhyolite is exposed in a wedge-shaped
outcrop which seems to plunge beneath the andesitie rocks to the northward, about 150 feet
north of the open-cut on No. 2 zone at an altitude of 1,865 feet.

Several hundred feet north of this point, and near the falls of Tulsequah creek, at altitude
1,950 feet, an isolated oxidized knob of rhyolite outerops through an andesite and on the west
side of the continuation of the dacite dyke. This outcrop is probably a spur from the northward-
plunging rhyolite. Southward, the rhyolite spreads out fan-shape in irregular contact with the
andesites and is intruded at intervals by basic dykes. At the Tulsequah River bank (altitude
165 feet) the rhyolite attains a width of several hundred feet, shows several phases of altera-
tion, and is strongly sheared and impregnated with pyrite.