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<br />:64 GEOLOGY AND ORE DEPOSITS OF THE FRONT RANGE, COLORADO
<br />rents contained as much as O.S ounce of gold. A ship-
<br />nent of high-grade ore, probably oxidized, contained
<br />7 ounces of gold and 11 ounces of silver to the ton .
<br />Telluride veins.-The telluride veins also have a
<br />northeasterly trend, but some of the most important of
<br />Item strike north-northeast artd dip west instead of
<br />outheast. They are younger than the pyritic gold
<br />ears, for in the Golden Age mine the Sentinel telluride
<br />'ein cuts the Golden Age pyritic gold vein. )\'Iost of
<br />he telluride veins lie in an outer zone h/l miles to tl
<br />Miles from the sodicgranite-quartz monzo»ite porpltyrp
<br />tock (fig. 77), but there are some exceptions; for ex-
<br />mple, the Buena group, an outstanding source of tellu-
<br />ide ore, is only three-quarters of a mile west of the.
<br />tock, and in the Stanley mine on the northwest border
<br />•f the stock sylvanite is found coating pyrite cubes in
<br />pyritic gold ore.
<br />The telluride veins range in width from a fraction of
<br />:n inch to as much ns 10 feet, and in the Buena mine
<br />ome ore bodies at vein junctions are ns much as 10 or
<br />ven 30 feet wide. The veins range in length from a
<br />'ew huuch•ed feet to more than a mile, but only small
<br />parts of the longer ones are productive.
<br />The veins contain gra}• jaspery (horn) quartz, finely
<br />lisseminated pyrite, and a variety of telluride minerals.
<br />(n some of the veins appteciable amounts of free gold
<br />.re associated with the tellurides. Commmdy the veins
<br />u~e made up of numerous interlacing scams of horn
<br />luartz, a fraction of an inch to 18 inches wide, in which
<br />he tellurides are unevenly distributed; the intervening
<br />wall rock is nearly barren. The most abundant tdlu-
<br />•ides in the district are krennerite (or calacerite) rnd
<br />tetzite, but there are also significant amow~ts of sylvan-
<br />teand altnite and small amounts of hessite, colorudoite,
<br />alive tellurium, and riclcardite (?). In most of the
<br />ears two or more telluride minerals are microscopically
<br />intergrown, and rarely is any one telluride exclusively
<br />resent. One outstanding exception is the ore frmn the
<br />Buena mine, where in nnich of the ore krennerite ap-
<br />>ears to be the only telluride, except for very snmil
<br />unouutso#petzite. i\finutegrainsoffreegoldarescat-
<br />ered through some of the tellurides, and apparently
<br />;old was the latest ore mineral deposited. eery small
<br />amounts of galena, sphalerite. and chalcopyrite are
<br />:onunonly associated with the telluride ore. rlssoci-
<br />~ted with the ore in the Rip \~an Daut, Bing Wilhehn,
<br />uul Gladiator veins are smmll amounts of roscoelite, and
<br />~.n the Jolut Jay vein there arc =_mall amounts of brown
<br />:arbonate.
<br />The telluride ores shoe a great range in grade, the
<br />grade depending mr what minerals are present and on
<br />~chether the whole vein is shipped or the high-grade
<br />horn quartz seams are sorted out. Large shipments
<br />have commonly ranged in grade from 0.5 [0 15 ounces
<br />of gold and 0.5 to 25 ounces of silver to the ton. The
<br />ratio of gold to silver depends ou the telluride minerals
<br />present and ranges ft•om 10:1 to 1: 2 but averages about
<br />1:1. Higlt-grade telluride ore sorted and shipped in
<br />sacks weighing 50 to several hundred pounds commonly
<br />ranges in tenor from 10 owtces of gold and 10 ounces of
<br />silver to as much as 28G ounces of gold and 40 ounces of
<br />silver to the ton. According to old timers, considerable
<br />amounts of ]tiglr-grade ore in the early days had a value
<br />of $5 to $10 to the pound.
<br />Size of ore shoots.-Most of the ore shoots in the dis-
<br />tr•ict are stnnll, commonly ranging from 50 to 200 feet
<br />in length, 30 to 100 feet in breadth, and It/z to 10 feet
<br />in thickness. Outstanding exceptions are [he Alice,
<br />tchich is a steeply prtcbntg ptpehke lead-silver ore body
<br />measuring 400 feet in length, 10 feet in breadth, and 5
<br />feet in [hichness; the Buena "big stope,' a telluride ore
<br />body about 150 feet long, GO feet in breadth, and 30 feet
<br />thick; and a compound shoat mt the Smuggler telluride
<br />vein, which had n pitch length of about 500 feet, a slope
<br />length of about 200 feet, anti a thickness of 1 to 3 feet.
<br />1'he shoots range in pitch from nearly horizontal to ver•-
<br />:ical, and the degree and direction of pitch depend
<br />largely on local conditions. 11'ithin man}• of the shoota,
<br />particularly in the telluride veins, there are small
<br />"pockets" of unusually high-grade ore, which commonly
<br />range from IO to 30 feet in length, 2 to 20 feet in breadth,
<br />and a few irtcltes to 18 inches in thickness.
<br />In the fluorspar veins and breccia zones the ore bodies
<br />=how n very great range in size. High-grade bodies have
<br />been small for the most part, ranging from 20 to 150
<br />feet in ]errgtlr, 10 to 100 feet in breadth, and I to 20
<br />feet in thickness. However, in recent ye:u•s, much larger
<br />bodies of lower grade have been mined in the breccia
<br />zones and some veins. These range from 150 to 480
<br />feet in lettgtlr, 120 to 350 feet itt breadth, and 3 to GO
<br />feet in thickness, and their full length has not yet been
<br />exposed. Iu most of them the long axis is nearly
<br />vertical. -
<br />llelation ofore to depth.-Ores in the Jamestoren dis-
<br />trict have been mined over a vertical range of about
<br />2,350 feet. The deepest workings are only about 500
<br />feet below the surface, and in many of the mines the
<br />workings are only 100 to 200 feet deep. In none of the
<br />mines accessible to the writers pace the veins been found
<br />to bottom with depth; in most of them the vein is as
<br />strong in the bottom level as at the surface. It there-
<br />fore seems probable that if structural conditions are
<br />favorable ore bodies mac Ue found well beneath the
<br />present workings. There is some evidence, however,
<br />that the early lead-sih'er ore bodies near the Porphyry
<br />.Mountain stock grade into pyritic gold ore at a depth of
<br />about 400 feet.
<br />li'oll-rock alteration.-Throughout the district the
<br />veins are bordered by zones of sericitic wall rock, which
<br />commonly extend a fc~c inches to 3 feet from the vein.
<br />In some places the veins are bordered U}' silicified wall
<br />rock, which also commonly forms a part of the vein.
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