Page 184 - The Geology and Ore Deposits of Sierra County, New Mexico - Bulletin 10

MINING DISTRICTS 181
continue into the Blue limestone beneath the stope. No. 14 shaft was sunk 100 feet south of the Twenty-five Cut tunnel and down the dip of the beds from the ore in Twenty-five cut toward the
rhyolite contact. This shaft cut the contact of the Crinoidal and Blue limestones at 63 feet below the collar, and manganiferous
flint was found in quantity, with occasionally enough silver for
assay, but no commercial ore was removed. Secondary processes had not enriched the ground along the dip of the beds this far
under the cover of Crinaidal limestone. Farther down the dip
of the beds, the Carolina shaft and workings prospected all the beds and contacts of that area, but no enriched ore was found,
although much primary mineralized chert was present.
East of Twenty-five stope is Thirty stope, 87 to 125 feet long down the dip and 8 to 37 feet in height. It was in solid ore,
which was very siliceous throughout. This ore body lay entirely within the Blue limestone, and except at the outcrop was entirely under a cover of Crinoidal limestone.
The beds dip more steeply in this area than at other places in the district and are sharply folded as a result of being dragged
against the rhyolite hanging-wall of the contact fault. Due to this folding and the attendant fracturing of the cherty bed and
surrounding limestone, the ore bodies were more massive and more siliceous in composition. A second important essential in
the location of these ore bodies was the fortuitous occurrence of these folded and fractured areas just at the line of contact with
an overlying bed or cover of Crinoidal limestone. Over the top of Thirty stope there is a large body of manganese-iron flint
which does not contain enough silver, except in patches, to war-
rant shipment at low prices for the metal.
The Boiler shaft, 150 feet north of Twenty-five stope, was
sunk on the Boiler Shaft fault, which strikes N. 50° E. and dips locally 80° SE. This shaft is 175 feet deep, and for 80 feet it passed through mud, which filled the fault opening and solution
cavities in the limestone alongside. It then cut Nodular lime- stone of the north wall for 58 feet and was stopped after pene- trating 37 feet of the topmost green shale member of the Percha
(Devonian) shale. The Nodular limestone was found to be slightly mineralized with pyrite and galena. The limestone-shale contact was barren.
Thirty stope continued eastward along the strike of the beds with greatly diminished dimensions, and merged with the Bridal
Chamber across this restricted neck of ore. The extreme eastern edge of Thirty stope and the greater portion of the Bridal Cham-
ber were covered with the porphyrite body shown in Plate X.
The Bridal Chamber ore body was a replacement of the Blue limestone. It extended 104 feet down the dip and was 20 feet
in maximum thickness, although the average thickness was nearer 7 feet, and it was worked along the strike for a distance