TUNGSTEN MINING AT TRUMBULL, CONN. 
By W. H. Hobbs. 
A deposit of tungsten ore of considerable economic importance is 
found at Trumbull, Conn. The ore occurs along the planes of contact 
between crystalline limestone and two bodies of hornblende-schist, 
the latter being a metamorphosed igneous rock. The tungsten min- 
erals (wolframite and scheelite) seem to be concentrated just below 
the contact of the limestone with the lower body of hornblende-schist, 
while in lateral distribution they are very variable. In 1898 exploita- 
tion of this deposit for the tungsten ores was commenced and was car- 
ried on until 1901, when operations were temporarily abandoned. 
The companies which managed the property carried out somewhat 
extensive mining operations, and expended considerable sums for 
buildings and machinery. 
The method of mining lias been to sink pits at the contact and fol- 
low down the tungsten-bearing zone. The larger blocks obtained by 
blasting are broken with sledges and the picked ore sent to the mill. 
The ore on reaching the mill is sent through a 15 by 21 inch Blake 
crusher, with a capacity of 10 tons per hour. This crusher discharges 
its product on the upper end of the picking table. An endless rubber 
belt acts as carrier and feeds to two small crushers on the floor below. 
These crushers deliver their product to two sets of Cornish rolls, 
running one-fourth inch apart and having a 22-inch diameter and 
16-inch lace From the rolls the material is elevated to the top of the 
mill and delivered \ o a pair of revolving wire screens 36 inches in diam- 
eter and 8 feet in length. These screens are one-eighth-inch mesh, 
and therefore refuse most of the material. A considerable portion of 
the dust is here drawn out by a current of air which passes under the 
screens. The material refused by the screens is carried by gravity to 
a pair of high-speed rolls, of 30-inch diameter and 18-inch face, run- 
ning one-eighth inch apart. From them it is returned to the elevator 
and again sent to the one-eighth-inch screens. All the material pass- 
ing the one-eighth-inch screens at either the first or second trial is 
sent to Wolf gyrating screens of three sizes, the mesh being 40, 60, 
and 90, respectively. 
Concentration is effected by a dry process, the Hooper pneumatic 
concentrator being used. This delivers a clean concentrate and leaves 
little ore in the tailings. Each machine is capable of treating 10 tons 
of material a day, and the yield of tungsten ore is said to be 5 per 
cent. The ore carries a little pyrite, which must be removed by 
roasting. No attempt is made at the mine to reduce the mineral to 
tungstic oxide. 
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