The Oro Fino vein is one of the two major veins of WEM. It is over 1.5 miles long, varies from 3 to 25 feet in width, and extends to at least the depth of the Sinker (2500 feet) where it is still well developed. The Oro Fino vein produced over $7M back when gold was $20/oz, or about $600M at today's prices. And there is plenty of gold and silver left.

Some quotes from the Piper Laney report (linked under President's DD):

That this type of vein is persistent is evident when one realizes that the Oro Fino-Golden Chariot vein has been actually mined for more than 3000 feet in length, and that where intersected by the Sinker tunnel, some 2500 feet below the surface, it is as strong as in the upper levels.

All of the larger veins, such as the Black Jack-Trade Dollar on Florida mountain, as well as the Oro Fino-Golden Chariot, the Poorman, and others on War Eagle mountain, are remarkable for their continuity along both strike and dip so far as developments have gone. The Black Jack-Trade Dollar vein has been developed for 6000 feet along its strike and for 1800 feet in depth without notable decrease in strength. The Oro Fino-Golden Chariot vein has a development along its strike of nearly 4000 feet, and is strong and well developed where the Sinker tunnel cut it, 2500 feet below the outcrop....On War Eagle Mountain are many .minor cross veins of much lesser magnitude, but even these, though in many instances very small, are surprisingly persistent.

Two veins dominate the system, the Oro Fino-Golden Chariot and the Poorman. Their relation to the second period of diastrophism has already been discussed in the section dealing with the regional structure. The first of these veins strikes N. 4° W. on the average, and dips eastward 80-90 degrees, although westward dips are not unknown. The system may be traced, with some interruptions, from the Great Western Mines Company's property (Pl. II, No. 55) southward for more than 1 1/2 miles to the Afterthoughtclaim (Pl. II, No. 68), and it retains its normal character in Sinker Tunnel (Pl. II, No. 56), more than 2,000 feet below the outcrop.

And from The Idaho Geological Survey Report:

The workings are on the northward continuation of the Oro Fino vein, which is a nearly vertical, north-south-trending quartz vein in the granitic host rock. Several other mines are on the vein, which has a length of at least 1.5 miles.

Statham (1998, p. 11) summarized the following history of the Oro Fino:
The Oro Fino Mine was the second vein ... discovered in the Owyhees, July 1863.
The first assay ... of the Oro Fino indicated over $7,000 per ton, mostly in gold.
In a chute of ore near the surface, the Oro Fino yielded to Tim Regan, one of the
mine[']s owners, $78,000 in less than 3 months. Mr. Regan purchased the Oro
Fino for $5,000 and later sold it for $750,000. This is one of the reasons that Mr.
Regan was the first of two millionaires to leave Silver City and settle in the Boise
Valley.
The Oro Fino Mine was developed through a shaft that was about 350 feet deep
and operated continuously from 1866 to 1876. There were a number of
production buildings, including a shaft house, covered dump tracks and a very
picturesque settlement at the Oro Fino. The mine operated at intervals for many
years and in 1885 and 1886 saw modest profits. This mine produced, throughout
its life, a total of about $ 2,000,000. . . .
The Oro Fino-Golden Chariot vein extends form the Great Western Mine, north
of the Oro Fino, south for about 1.5 miles to the Afterthought Mine. The vein
varies from 3 to 14 feet wide and retains its character at a depth of 2,000 [feet]
below the surface exposures. The mines that are on the vein comprise what is
called the Oro Fino Group and include the Oro Fino, Ida Elmore, Golden Chariot,
Minnesota, South Chariot and the Mahogany. These mines were developed from
shafts located on small claims with the upper levels producing high-grade ore and the lower levels maintaining good values in the ore. The mines of the Oro Fino
Group were rich producers and actively worked until the crash of 1875. Although
there was some work done in these mines for the next 20 years, they never went
into serious production after 1875. During the life of these mines the Oro Fino
Group produced an estimated $ 7,000,000.