Gold-bearing sedimentary rocks in northwest Wyoming — A preliminary report

Abstract

Thick sequences of gold-bearing quartzite conglomerate occur in latest Cretaceous and Tertiary formations and in Quaternary gravels derived from them in northwest Wyoming. Analyses of about 1,200 samples (by a new cyanide-atomic absorption method) and 750 panned concentrates representing 53 localities show the following averages in parts per billion and cents per cubic yard: Harebell Formation (latest Cretaceous), 65 (11 cents); Pinyon Conglomerate (Paleocene), 86 (14 cents); Fort Union Formation (Paleocene), 35 (6 cents); conglomerate of earliest(?) Eoceneage, 94 (14 cents);WindRiverFormation(early Eocene),222 (35 cents); Pass Peak Formation of Eardley and others (middle(?) Eocene), 47 (8 cents); Miocene(?) conglomerate, 65 (11 cents); Quaternary deposits, 103 (16 cents). These values are for the bulk rock although the gold is largely confined to sandstone layers and the sandy matrix of the conglomerates, which contain various proportions of pebbles and cobbles. The conglomerates were derived chiefly from Precambrian and possibly Paleozoic quartzite in a now-buried uplift northwest of the Teton Range. Although the grade is low, the volume, 50 cubic miles or more, is so large as to constitute a resource of enormous proportions. The presence of above-average grades in some localities suggests that local concentrations may exist and makes the conglomerates and their derivatives attractive for additional prospecting.

Gold and uranium potential of the Wind River Formation on the Wind River Reservation, northwestern Wyoming

“…11). This coincidence could have been predicted because, based on clast lithology and shape, the source of the conglomerates had to be the late Cretaceous and Pal eocene auriferous quartzite roundstone conglomerates of the Jackson Hole area that were described by Lindsey (1972), Antweiler and Love (1967) and Love (1973). The source of the conglomerates, for the most part, lay west of and outside the present Wind River Basin and thus they could be expected to be distributed along the basin axis.…”

“…The source of the auriferous Harebell and Pinyon roundstone conglomerates was a previously existing uplift northwest of the Teton range in eastern Idaho called the Targhee uplift (Antweiler and Love, 1967;Lindsey, 1972). The Targhee uplift was perhaps only the penultimate source of the gold.…”

Reconnaissance study of the Wasatch, Evanston, and Echo Canyon Formations in part of northern Utah

“…The conglomeratic sequence, which is divided into the Echo Canyon (Late Cretaceous), Evanston (Late Cretaceous and Paleocene), and Wasatch (Paleocene and Eocene) Formations, was derived principally from rocks exposed in Late Cretaceous and early Tertiary folds, thrust plates, and normal fault blocks along the north-central Wasatch Mountains. Much of this conglomerate is somewhat analogous in structural setting, type of source rock, and environment of deposition to the gold-bearing Pinyon Conglomerate of northwestern Wyoming (Antweiler and Love, 1967). The rocks in northeastern Utah were sampled to determine if the formations contain placer gold similar to that in the Pinyon Conglomerate and if the source rocks might contain unrecognized pre-lower Tertiary deposits of gold coarse enough to form placer deposits.…”

A mechanical panning technique for separation of fine-grained gold and other heavy minerals

“…after much trouble the surfaces are wetted and the gold is got under the water and on to the top of the sand, the first wave from the other side of the pan over the sand floats the gold again." Later, Antweiler and Love (1967) reported experienced panners recovered only about 18 percent of the total free gold analyzed in gravels of the upper Snake River in Wyoming. Hill (1916) described similar difficulties when other gravity techniques were applied.…”