98

Although evidence is not at hand to prove beyond doubt that the ore- bodies replace both diorite and porphyrite as well as limestone, yet the field evidence strongly substantiates this view. In numerous instances both within and close to the ore masses, it is possible to observe what appears to be examples of all stages in the replacement of respectively diorite and porphyrite and at the same time there is a complete lack of any direct evidence of the former presence of limestone.

ECONOMIC CONSIDERATIONS

At the Prescott mine there has been exposed a number of bodies of magnetite occurring within a limited area. A nearly worked out mass resting on limestone occurs in the east, high up on the face of the highest open working. This body gives no prospect of affording any considerable amount of ore.

A second ore-body is partly exposed in the hill-side at the west face of the higher quarry. It possibly extends for some considerable distance westward into the hill over which outcrops highly altered diorite, in part richly impregnated with magnetite. The body may extend downwards with expanding dimensions; it may connect with the large magnetite body exposed less than 100 feet to the west. There is, however, no availa- ble evidence indicating that the mass of magnetite may be anything more than a relatively small body.

The large body of magnetite in which the lower quarry has been opened has an area of 7,500 square feet. The boundary on the east side follows a nearly vertical plane to a height of at least 60 feet and it is possible that all boundaries are essentially vertical, that the shape of the mass is pipe-like, and that it extends downwards along a general vertical direction. From the floor of the quarry to the highest part of the mass is 125 feet. The amount of ore partly developed above the floor of the quarry, assuming the boundaries to be vertical, is estimated to be not greater than 50,000 tons. The depth to which this body may extend is unknown. Some who have examined this deposit! are of the opinion that this body extends downward to unite with the ore struck in the end of the tunnel 255 feet below the level of the quarry floor. One former

observer* on the other hand states . . . . “sufficient development work has not been done to determine if the bodies exposed in the quarries are connected with one another and with the one inatunnel”’. . . . An

inspection of the plan and sections of the mine (Figure 16) reveals that the ore penetrated by the tunnel lies in front of and to one side of the exposure of ore at the surface. Where the tunnel enters the ore-body the boundary of the ore mass follows a general northeasterly course and it is not im- probable, therefore, that the body of ore extends a considerable distance to the west and, also, since the tunnel face is still in ore, it is also possible that the mass continues northward a considerable distance. If both pos- sibilities should prove to be actualities, a considerable part of the 1 McConnell, R. G.: Op. cit., p. 88.

re Pee, Is.: “Iron Ore Deposits of Vancouver and Texada Islands, B.C.”; Mines Branch, Dept. of Mines, Sanada. a ee eee “Iron Ore Deposits on Vancouver and Texada Islands, B.C.”’; Mines Branch, Dept. of Mines, ull. } » p.d2. Whittier, W. H.: ‘‘An Investigation of the Iron Ore Resources of the Northw est’’; Univ. of Washi e of Industrial Ri rch, Bull. No. 2. : ‘ Seen eee

2 LeRoy, O.I Preliminary Report ona Portion of the Main Coast of British Columbia and Adjacent Islands, ete.”’; Geol. Surv., Canada.