9
AURIFEROUS GRAVELS.
Swauk district. —The Pleistocene gravels alongSwank Creek and many of its tributaries are goldbearing. These alluvial gravels form the terraces,which are especially prominent and extensive atthe junctions of Swauk and Williams creeks and ofBoulder and Williams creeks. The gravel depos-its are from a few feet to 70 or 80 feet in thickness,and while red or yellow at the surface, the gravel isblue below. The upper portions of the gravelalso are less easily worked, since induration of thegravel has followed the oxidation of the cement-ing material.
While fine gold is found throughout the graveldeposits at some localities, most of the gold occursclose to bed rock and in channels other than thoseoccupied by the present streams. The markedcharacteristic is coarseness. Pieces several ouncesin weight are common, while a number of nuggetsweighing 20 ounces or more have been found, andone or more nuggets of about 50 ounces have beenreported, the largest nugget of the district havinga value of $1100. These larger nuggets are usu-ally well rounded, but on the tributary streamswire and leaf gold is found. The gold is not pure,containing considerable silver, which materiallydecreases its value.
The bed rock, which belongs to the Swauk for-mation, is usually of a nature to favor the collectionof the gold. The inclined beds of hard shale formnatural “riffles,” and from the narrow crevices inthe shale the best nuggets are often taken. Thesandstone beds wear smooth, in which case the bedrock is apt to be barren. The old channels, bothof Swauk Creek, and of its tributaries, vary some-what in position from the present course of thestream, but only within definite limits. The oldvalleys and the present valleys are coincident, but,within the wide-terraced valleys of the present,older channels may be found, now on one side andnow on the other. Thus, on Williams Creek andthe lower portion of Boulder Creek the old water-course has been found to the south of the presentchannel of the stream, and is in other cases belowthe bed of the creek. On Swauk Creek the depositsworked are above the level of the stream, beingessentially bench workings. Here hydraulic plantshave been employed, but elsewhere the practice hasbeen to drift on bed rock. While the endeavor isto follow the old channels, it is found that the“pay streak” can not be traced continuously.Ground that will yield $40 to the cubic yard ofgravel handled may lie next to ground that doesnot contain more than 50 cents to the cubic yard.In the last few years the operations in the Swaukbasin have been on a larger scale. Williams Creekhas been dammed and methods have been devisedto handle the tailings and bowlders on the lowercourses of Swauk Creek, where the gradient of thevalley is low.
The source of the alluvial gold is readily seento be the quartz veins known to occur in theimmediate vicinity. These will be discussed in afollowing paragraph. The noticeable lack ofrounding of much of the gold shows that it hasnot been transported far, and indeed the limitedarea of the Swauk drainage basin precludes anyvery distant source for the gold. It is only alongthe Swauk within a few miles of Liberty and onWilliams Creek and its tributaries that gold hasbeen found in paying quantities, and, as will benoted later, this is approximately the area in whichthe gold-quartz veins have been discovered. Fromthe outcrops of these ledges the gold and quartzhave been detached and washed down into the bedsof the streams, where the heavier metal was sooncovered by the rounded bowlders and pebbles withwhich the channel became filled. The conditionsunder which the gold was washed into the streamsprobably differed little from those of to-day, exceptthat the streams were then filling up their valleys.
Peshastin district. — The gravel deposits in thevalley of the Peshastin are less extensive than inthe Swauk district. The alluvial filling of thecanyon-like valley of the upper half of PeshastinCreek is not so deep and does not show the well-marked terraces so prominent in the Swauk Valley.The gravel appears to be gold bearing throughout,and the gold is rather uniform in distribution. Thelargest nuggets are found on the irregular surfaceof the pre-Tertiary slate which forms the bed rock.While the largest nuggets found in the Peshastinplacers are less than an ounce in weight, and there-fore not comparable with some of the Swauk gold,the Peshastin gold is fairly coarse and easily saved.
Mount Stuart.
The gold is high grade, being worth about $18 anounce.
The principal claims on the creek, below Blewett,are owned by the Mohawk Mining Company, whichis hydraulicking the gravels with water from theupper Peshastin and from Negro Creek. Workwhich has been done on Shaser Creek shows thegravels to be gold bearing, and here also the goldis high grade. This fact is interesting, since, whilethe Shaser Creek drainage basin is almost wholly inthe same formation as that of the Swauk basin, thegold found in the two creeks is quite different, theSwauk gold containing a considerable amount ofsilver.
Stream gravels in other parts of the quadrangle,notably on North Fork of Teanaway and on Staf-ford Creek, have been prospected, but no gold hasbeen found to warrant further work.
GOLD-QUARTZ VEINS.
Peshastin district. —A few mines in the vicinityof Blewett have been producers for about twenty-five years. The many changes of management andmethods of operating these properties, however,make it impossible at the present time to determineaccurately the character of the ore that has beenmined or to estimate even approximately the prod-uct during this period. Much of the ore has beenlow grade, and the gold has been extracted bymeans of arrastres, stamp mills, and a small cyanideplant, but not always with very successful results.The small stamp mill first built in this district wasthe first erected in-the State of Washington . An-other mill, with 20 stamps, has lately been rebuiltunder the Warrior General management.
The best-known property in the district is theCulver group, comprising the Culver, Bobtail, andHumming Bird claims, and now known as theWarrior General mine. This mine in its geologicrelations and vein conditions is typical of the minesof the district. The country rock is the alteredperidotite or serpentine, which exhibits the usualvariations in color and structure. The WarriorGeneral and the other mines are located in a zoneof sheared serpentine, where the mineral-bearingsolutions have found conditions favorable for oredeposition. This mineral zone has a general east-west course, and extends from east of Blewett acrossthe Peshastin, up Culver Gulch, and across to thevalley of Negro Creek.
The Warrior General vein has a trend of N. 70°to 80° E. and is very irregular in width. In thewalls the serpentine is often talc-like in appearance,while the compact white quartz of the vein is some-times banded with green talcose material. Sul-phides are present in the ore, but are not at all prom-inent. The values are mostly in free gold, whichis fine, although in some of the richer quartz theflakes may be detected with the unaided eye.
The workings in this mine consist of a numberof tunnels driven at different levels in the northwall of Culver Gulch. These follow the vein fordifferent distances, the vertical distance betweenthe lowest tunnel (No. 9) and the highest openingof importance (No. 5) being about 650 feet, andconnections have been made between most of thelevels. The vein is approximately vertical, althoughit has minor irregularities. The quartz is 7 to 8feet in width in some places, but pinches in others.In the upper tunnel, No. 5, the ore appears to bebroken quartz of. the same character as that in thelower tunnels, occurring here much more irregu-larly, although the richest ore has been taken fromthe upper workings. Some very rich ore bodieshave been mined, but they are small and their con-nections have not been traced. The most extensivework has been done from the lowest tunnel, andthe latest work here shows that the serpentine,which is so much broken in many parts of thismineralized belt, is here more solid, a remarkablywell-defined and regular wall having been followedfor over 300 feet.
Other properties in the same zone as the WarriorGeneral are the Polepick, Peshastin, Fraction ,Tiptop, Olden, and Lucky Queen. These have allproduced ore which has been worked in the Blewettmill.
An interesting feature in the geology of CulverGulch is the probable existence of a fault. On thenorth side of the gulch, at an elevation of about3750 feet, and near tunnel No. 5, a large basaltdike, 25 feet wide, is very prominent. This dikehas a trend of N. 26° E., but its continuation is notseen on the south side of the gulch. Fifty feetlower on the south side of the gulch, however, asimilar dike occurs with a trend of N. 50° E., but
this in turn can not be detected at the point whereit ought to outcrop on the north side. If these areparts of the same dike, as seems probable, there hasbeen faulting. Such a fault would cross the Culvervein at a low angle and probably between tunnels5 and 6. The broken character of the ore in theupper tunnel indicates that movement has modifiedthe vein at this point, and such movement may beconnected with this supposed fault. At the time ofthe examination of this mine, connection had notbeen made between tunnels 5 and 6, and therelations of the dike to the ore body could not bedetermined. If the dike interrupts the vein, themineralization is pre-Eocene in age; while, on theother hand, if the vein continues through the 25feet of basalt, even although it may vary in char-acter with the change in the wall rock, or if thefissure in which the quartz has been depositedfollows the plane of the fault which it is believedhas displaced the basalt dike, then the period ofmineralization is not earlier than late Eocene , andthe Peshastin gold-quartz may be of the same ageas the veins of the Swauk district, a descriptionof which is given below.
Negro Creek district. —Although this region is acontinuation of the Peshastin mineralized zone, noclaims in this district have become producing mines.The region has been prospected for many years anda number of small veins have been located, andsome ore worked in a small mill and in arrastres.The ore is mostly quartz with some calcite andsulpliurets. The veins are irregular and the wallrock is generally serpentine, much of which issheared and jointed. Many of the locations havebeen on the red or yellow “nickel ledges” to whichreference has been made; on page 4 is given ananalysis of this rock, which has been considered bymany prospectors to be itself an indication of ore.
Swauk district. —The gold-quartz veins of theSwauk are very different from those in the vicinityof Blewett. They are in part narrow fissure veinsof quartz with some calcite and talcose material, thewall rock being the sandstone or shale of the Swaukformation, of Eocene age, or in some cases a diabaseor basalt dike may form one wall. Quartz stringersrunning off from the vein are common, and at onelocality thin bands of quartz follow the beddingplanes of the sandstone. A peculiar type of veinmaterial is locally termed “bird’s-eye” quartz.This occurs in several mines, and may be describedas a friction breccia in which the angular fragmentsof black shale are inclosed in a matrix of quartzand calcite. The quartz shows radial crystallizationoutward from the separated fragments, and oftenopen spaces remain into which the small crystals ofquartz project. The walls of such veins are some-times sharply defined, but in other cases manysmall veins of quartz traverse the shattered wallrock in every direction, so as to render it difficultto draw the limits of the vein itself. This transi-tion from the peculiar type of vein into the shatteredrock shows the “bird’s eye” quartz to be due tobrecciation along more or less well-defined zones,followed by mineralization.
The “bird’s-eye” quartz has its gold content veryirregularly distributed. The values are mostly infree gold, with a small amount of sulphurets present.The gold occurs in fine grains within the quartzor next to the included shale fragments, and theapproximate value of the ore may be readily foundby panning, while in many cases the gold may beseen on the surface of the quartz, in the form ofincrustations of leaf or wire gold; and in a specimenfrom the Gold Leaf mine perfect octahedral crystalsof gold lie upon the ends of the quartz crystals.The silicification sometimes extends into thecountry rock, and some values are found there.The gold of the quartz veins, like that of thegravels, is light colored and contains a considerablepercentage of silver. In the Little York this silveris reported as amounting to about 20 per cent.
The quartz veins that have been opened in theupper basin of Williams Creek have a generalnortheast trend, being thus roughly parallel withthe basalt dikes. In the Cougar the hanging wallof the vein appears to be a badly decomposedbasalt dike, while the Gold Leaf has one veinwholly in sandstone and shale and another in alarge diabase dike. The relation of the veins to thedikes is therefore not constant, but it may be notedthat the fractures which have been filled by thevein material are usually approximately parallel tothe fractures in the vicinity which have been filledby the intrusion of basalt. That there has beenmore than one period of fracturing, and that theperiod of mineralization was not exactly contempo-
raneous with the time of igneous intrusion, is shownby the occurrence of veins cutting the dikes them-selves. It is probable, however, that the two pro-cesses occurred within the same geologic period andthat the ore-bearing solutions derived their heatand possibly their mineral content from the intru-sive and eruptive basalt of the area.
A number of quartz veins on Swauk, Williams,Boulder, and Baker creeks are being prospectedat the present time, and in view of the richness ofthe alluvial gold which has been derived from theveins in this vicinity it would seem that the pros-pecting is well warranted.
COPPER AND SILVER.
In the Negro Creek district both copper andsilver occur with the gold in the veins already de-scribed. Many of the ores are essentially copperores, but whether the bodies are extensive enoughto warrant their development has not yet beendetermined. This copper belt extends westwardalong the headwaters of North Fork of TeanawayBiver and of Ingalls Creek, but at only one localityhas any large amount of ore been mined. TheGrand View mine, situated on the east side ofFourth Creek about 3 miles southeast of MountStuart, has produced some native copper. Thevein is in a zone of sheared serpentine, and, as faras could be determined from an examination of thedeserted workings, the ore body is very irregular.With the native copper is the red oxide, or cuprite,and the ore is reported to carry varying amountsof gold.
There have been some prospectors at workrecently in the vicinity of the forks of TaneumCreek, about 5 miles south of Clealum, and coppersulphides are reported to have been found. Thecountry rock here is the Easton schist and is every-where more or less seamed with quartz.
As has been noted above, the gold of the Swaukdistrict is argentiferous, the percentage of silvervarying with the locality. No other silver ores areknown to occur in the Mount Stuart quadrangle.
NICKEL AND QUICKSILVER.
Nickel is a metal frequently reported in theassays from the Negro Creek district. Its presencein small amounts in the serpentine which is of suchimportance in this area is shown by the analysisgiven on page 4, and this renders it probable thatsome nickel ores may be found. The peridotiteand serpentine resemble closely the peridotite atRiddles , Oreg., where deposits of nickel ore occur.The green silicate of nickel, genthite, which isthe ore at Riddles , was not detected, however, atany place within the area of serpentine in thisquadrangle. The analysis of the “nickel ledge”given on page 4 shows a smaller percentage ofnickel even than that contained in the serpentineitself.
Cinnabar has been found at a few points at thehead of Middle F ork of Teanaway River. In a pros-pect on the western edge of the quadrangle thecinnabar occurs along a joint plane in the alteredrock of the Peshastin formation. The richness ofthe ore is evident, but the fact that such bands ofcinnabar are very thin may prevent the depositfrom being of economic importance.
Roslyn basin-. —The most important mineralresource of Kittitas County is coal. The Rostynbasin is one of the most productive coal basins onthe Pacific coast and it is included mostly withinthis quadrangle. The coal occurs in the upper partof the Roslyn formation, and the extent of this pro-ductive portion, together with the location of mines,is shown on the economic geology map. Theupper beds of the Roslyn formation have beeneroded except in the center of the basin, so that thecoal field is limited to the immediate valley of theYakima between Ronald and Teanaway. The out-crop of the Roslyn coal has been traced along thenorthern side of the basin, so that the outline hereis accurately determined. On the southern side,however, the deep gravel filling of Yakima Val-ley conceals the rocks beneath, and this boundaryof the basin as mapped is based wholly upon dataderived from observations of the structure madeelsewhere. As shown on the map, there are between10 and 12 square miles of coal lands in theMount Stuart quadrangle.
The structure of the Roslyn basin is simple.The dip of the coal beds is low, 10° to 20°, and nofaults have been discovered in the basin. Its axispitches to the southeast, and since the fold is