From Dines:

Tregrehan is a detached mine half a mile N. of New Wheal Eliza.

[…]

Tregrehan Mine, sometimes called Tregrehan Higher Mine to distinguish it from New Wheal Eliza, also called Tregrehan during the latest workings, has three lodes, North, Main and South or Blackberry, all coursing E.-W. and underlying 40 ° to 50 ° N.

According to the plans (dated 1893 and 1913) the amount of underground work is small. Adit Level on Main Lode commences just east of the road in the valley, 200 yds. N.E. of Boscoppa farm, and extends 200 fms. E. Main Shaft, 170 yds. E.N.E. of adit portal, is vertical to the 20-fm. Level where a crosscut 10 fms. S. meets the lode. The 10-fm. Level on Main Lode extends 55 fms. E. and 20 fms. W. of the shaft crosscut; the 20-fm. Level is short. The amount of stoping is not known. The shaft passes through North Lode at adit level (26 fms.) but this lode has not been developed. South Lode, underlying 50° N., is crossed by several south-dipping slides, some of which heave it upwards a few fathoms on the north. Incline Shaft, 270 yds. S. by E. of Main Shaft, follows the lode to the 20-fm. Level, which extends for 50 fms. W.; there are shorter drives at shallower depths, east of the shaft on which there are small stopes. A crosscut from 20 fms. W. of the shaft on the 20-fm. Level connects with Main Shaft.

1889-1893: 10.5 tons of black tin; 1909 3 tons of black tin.