Burlington Mine, Jamestown District, Boulder Co., Colorado, USA

REF:Deposit:: LOVERING & GODDARD, 1950, USGS PP 223, PG 274
Deposit:: SIMS AND SHERIDAN, 1964, USGS BULL. 1159
Deposit:: ARGALL, 1949, COLO. SCH. OF MINES QUART., V. 44, NO. 2, P.182
Deposit:: 3A) GODDARD, COLO. SCI. SOC. PROC., V. 15, NO. 61 P.36-38, PL
Deposit:: MINE MAP REPO # 402332, 403956 404114, 404632, 404633, 40
Deposit:: 405047, 405052, 405053, 405054 405055, 405224
Deposit:: OWN/ ALLIED CHEMICAL CORP REF. VA VANERWILT MINERAL RES OF C
Deposit:: REF USGS PROF PAPER 223 PLATE 3.
Commodities (Major) - Uranium, Fluorine-Fluorite
Development Status: Producer

The Burlington Mine was a major producer of fluorite from about 1940 thru 1973. The mine worked a large, nearly vertical, roughly elliptical breccia pipe at least 50-60 feet wide and 200 feet long. This breccia pipe was developed in Precambrian rocks just beyond the northern edge of a Tertiary granodiorite stock and the western edge of a younger, much smaller stock of quartz monzonite porphry. It contained massive granular fluorite with angular fragments of altered country rock and massive sulphides. Some of the fluorite was a relatively pure, cohesive mass of angular purple fragments ranging from 1/2 inch downward. In other parts of the orebody the fluorite was pale purple to nearly white. This material had more fine grained matrix which contained impurities (rock flour?, clay?, quartz?) that gave it a brownish overall color. The sulphides were mainly argentiferous galena and pyrite or chalcopyrite. Fragments of both the country rock and the sulphide ranged up to a few inches. Multiple episodes of mineral deposition and brecciation does not seem to have produced vugs.

At the beginning of February, 1970, this author and a college friend, having just registered for our last undergraduate semester at the Colorado School of Mines, decided to head for the hills on a fine, mild winter day. By chance we came across the then active Burlington Mine. We asked if we could look around the dumps but were offered an underground tour.

All the activity was on the deepest level, the 1500 foot level as I recall. It was hot , very humid and oppressive. We didn’t get to see the active stopes and I forget exactly what stoping method was in use. I believe it was some variation of sublevel stoping. Fortunately, the crosscuts contained good exposures of the ore, probably as good as or better than we’d have seen in the stopes, with a lot less bother. The mine foreman was very obliging and hammered off fragments of whatever we wanted a sample of. He told us that the mine was near the end of its life. All the ore above 1200 or 1300 (hard to remember after nearly 40 years) had been mined out and when mining the remaining block between there and 1500 was completed that would be it. It wasn’t economically feasible to extend the shaft to greater depth. The developed part of the orebody was exhausted about 31/2 years later and the mine was closed.

On the way back up to the surface we stopped at one of the other levels (1200?), the deepest completely mined out level. It was dramatically cooler and less humid. We walked into a crosscut that ended very abruptly at a huge void. The light from cap lamps was quickly swallowed by the darkness but we could make out the far side of the mined out stope some 60 feet away. The top of the remaining ore block was 100 feet below and irresolvable in the blackness. I don’t remember a yawning crater at the surface and there was certainly no surface light at depth. There must have been a near surface pillar of significant thickness. Even though there wasn’t a direct opening to the surface the void of the mined out breccia pipe had great vertical extent and enabled far better ventilation.

The Burlington Mine was not a producer of attractive specimen material. Only a geologist and a mining engineer could love the samples we collected. It was a great day.