44 M I N E S AND MINER,\L RESOLRCES.

clrifting 11acl started from there. Another ~ i n z e sunk fro111 the 1600- foot n o r t l ~ drift I d reached 1800 feet, fro111 which level a drift struck good orc This winze will Iw contin~led to nwet a raise fro111 the 2700- foot level. The Champion shaft in recwrt years has also reached a tlepth of 2700 feet (inclined), 1)ut the 1:ral vein has evidently not come u p to esprctiltion. I t is said the Chnnrpion ore-shoot was bottomed a t about 1200 feet. Ore recently n~iued (1913) from the Ural vein has cwne nrostly fronl the Sevada Cit!- ore slroot which IS connected with the Clranipion shaft a t tlw 1000-foot level by n drift nearly a mile long. This sl~oot on tlw latter 1rvc.l shou c~ l it tl~icliness between walls of 2 to 4 feet ant1 in p1act.s the 1111artz \\.as thickly matted with sulphides of gootl gri~tlth. Tlrt. Clrampion and Sevacta City shafts have in the past two yearb I)ecome auxiliary sh;~fts and the Providence shaft is used for I~oisting ore.

TIIP ore f r o n ~ this gronp of wines t'arries no specimen gold. The >~ilpllicles awrage (iC;{. or nlore of tlrr ore ancl carry :30% of the vahie. Ahortt SOT of the. gold is saved by cyanidin<, the balanre by outside I I I I ~ ; I I I I ~ I ~ I ~ . This will pr01)ilI)ly lead ultimately to the introduction of t I t c h floti~tion prowsq. w11ic.h h;is been tc~stcd here. and is thought ilpplic;ll)lt~ to the ore.

Tlir l'ittshnrg vein. striliiu~r S 4.5' E. , I I ~ dippin% 43 S E . ; and tlit. Goltl I'lat or I'otosi vein. \\it11 nortl~erly strike and dip of 40' E., arc1 now c~ontrolletl by the Pittsl~nrc-Gold F la t Company. The shaft 11i1s lwen p ~ t t clown to a tlrpth of 162.5 feet on the P i t t s h r g vein. The ottly \\-ol.li of importirnw s inw thv 1)ocly of this report mas written has 1 1 t w 1 ; ~ n i~ttempt to find tlw Croltl F la t vein from the Pittslmrg shaft. On the SI I I .~~I ( 'C tire wins arP a l m ~ t 1000 fret apart. and i t ~v;is tliouqht to 1w ;I sintple ntnttcr to connect them ~~nt lcrground hy crowxtt ing iilong tllo l i w of one of the post-n~int*r;~l fi~ults. I t is reported that a 1!3IO-foot vrosscwt fro111 thv 1:~I)o-fcot 1 1 ~ 4 of the l ' i t t sh~~rg shaft to\v;trtl tltv (:oh1 F l i~ t failed to tlisvlow tlw latter vcin.

Bibliography.

Reports of tlie State JIineralogist. from 1886 to 18'36. Folios of (:eologic Atlas of the Vnited States, U. S. Geological Survey, Stw. 18, 29 and 66. Seventeenth Annual Report, U. S. Geolog- ical Survey, part 11, pages 13 to 262. The Gold Quartz Veins of Sevada City and Grass Valley Districts, hy W. Lindgren. li. S. G. S. Prof. Paper 73, Tertiary Gravels of the Sierra Sevada, by W. Lindgren, 1911. 17. S. G. S. Mineral Resources of the ITnited Stz~tes for the Years 1905 to the Present.

NORTH BLOOMFIELD MINING DISTRICT.

Including the region about North Bloomfield. Columbia Hill. Malakoff, Rel~ef, Lake City, Snow Tent, Moore's Flat. Orleans, and Snow Point.

This district occurs in the c e n t r ~ l part of Neviida C'or~nty, 14 miles ~lortheast of Nevada City. The nearest shipping point is S c ~ u d i i City, terminus of the Nevada County Narrow Gauge Railro~td, 14 rnilrs 1)y a i a i r road which crosses the South Fork of Yubn River irt it point 3 n d r s southwest of North Bloomfielcl. The elwittion of Sort11 I3loo1iifield is 3200'.

The district occupivs the divide I)vt\vren the JIidcllt. i ~ n d Soitth Forks of Yuba River. T l ~ e elinlute is temperate \\-it11 dry, \\-art11 slitlltliers, and heavy rains with some snow ill winter. The ll~ntbcr industry is important since the region is within the forest b ~ l t of thr Sivrrii Sevilda. r 1 lliere is a n abundn~ice of yello\v i u d sltzitr pint,. .spr~tw i~nrl tir, with oak a t lower elevations.

Gold is obtained extensively in Tvrtiirry river gr;ivels iincl thr 111-0-

duction is reported to have I w t i $!.3)t).OO0 rip to the !thirr I!)()().

Hirtory of mining.

Hydraulic n~ in ing has been currletl on , ~ t Sorth I3loomtieltl on n very iwge sctile. Excavi~tions from .NO' to 1' i t 1 width. t ~ s t ~ n d for 5000' and reach u depth of XO'. The clrposit I I ~ I S 1wc.11 o l~v t t t~ l I)y a Iwlrock tunnel 7874 fert Ion:: with cntrllnce in IIIIIIIIIIIL. (';~iion. This t ~ ~ n n r l together with other preliminary work is said to hive tlost $3,000.000. Soon after its completron hydn~ulic mining \\.;is I~intlrretl by i~nti-clel)ris legislation and only such gravc~ls hrtw I)rw \\orIic~tl n I~osr t;~iiings codtl be impounded before reaching the rlvcr.

The gravel p r o d ~ ~ c e s on tlw ~ v c ~ r i ~ g t ~ of 4# to 104 prr c~tbic ycl., tlic~ richest portions lyin:: new bedrock. Tlre y idd I)rtuvrn the yertrs 1866 and 1900 was approximately .J;:I.T,Ol).0OO. from tltr S0.000.OOO cu. ycls. excavated. I t is estimated that 1:30.000,000 1.11. ytls. rctnain. A siniili~r yardage occurred to the west, near Lake C'ity.

At the Derbec mine, one mile due north of Sortli Bloomfielcl. 2 1 shiift and workings have exposed a deep channel extenclinq several thousand feet eastward. This channel connects with the milin one of the region and has been mined for 7000 feet ripstrenm from the shaft. The mine was operated from 1877 to 1893, and the production often reached $200,000 per year.

Hydraulic work was formerly ( w r i e d on a t Rrlief, \vhc>re drift mining is now being pursued. The Union tunnel. 2500' long. is reported to have yielded from $30,000 to $90.000 iinnrially for a nlilnber of years.

Water is ~ t~ppl ie t l l)y the Stwt 11 I~loon~lit~ltl ~ I ~ I - I I , w r r ~ 1111: 3200 miner's inches from Bowman Lake.

54 MINES .\ND MIXERIT> RESOURCES.

the gravel cl~anilel of North San Juan. This deposit is probably of an earlier period than the Tertiary griwels.

I n the I~r l t of ampliibolite schist extencling from Bircl~ville north to I{nllards Bar severill clnartz veins llnve been found carrying artriferous i r o ~ ~ ant1 copper pyrites. One of the larger veins strikes north and tiips 60" E.

ROUGH AND READY MINING DISTRICT.

Tlterr is ;I cood water s ~ ~ p p l y Squirrel ('reek. Deer Creek, nncl ('ltwr C'rtv,li tlow nvst to Y11l);t liivcr. Ditc.llrs of the Sonth Yuba ('ilt~ill C'o111pi11iy ('itrr>. w a t ~ r from t l t ~ Ire:l(l~vntcrs of South Puha River

t o (;t.i~s< Y:tII(y for r~tiiling i~ncl othw purposca.;. Electricity may be 11st~1 for pou-er.

History of mining.

In the y13i1r 15!)1 it was rc.portc11 that :1.000.000 cubic yards of gravel 11i11l I ) O C I I ~ \ t ~ i ~ ~ i ~ t ~ ( l ilt 1io11~'Il i111tl Tlvady and Randolph Flat, ant1 tliat

1 . . I I S r i i t a i l a l l . 111 1909 the total protl~iction t ~ f tilt, h y ~ l r i ~ ~ ~ l i c ~ n~inl..; ilt R O I I ~ I I at111 Renrly, Frtlnch Corral, Smartsvillc it1111 Crass Valley ~vns only $8,000.

Bibliography.

Tlintl~rcn. W.. T c r t i i ~ r ~ Cril~rels of tltc Siwra Nevada. U. S. Geol. Survry. Prof. Paper So. 7:i. pp. 120-124. IT. S. Gcol. Survey, 3Iinc.rill Resonrces, 1907. pt. 1. p. 215. U. S. Geol. Surrey Folio No IS. 1895.

Topography.

I'lt(1 r c y i c ~ ~ ~ i r t ficnvt.ill is I)rokc~n 11y ,"rorll)s o f hills, none higher than 2500' al)ovt1 seir Irvel, which separate iL series of parallel westward

NEVADA COUNTY. 55

flowing streams. Squirrel Creek flows northwest throllgh Penn Valley

to r point a mile west of Avthuny IIome, where i t joius Deer Creek. Northwest of Penn Valley the ground slowly rises to hills 500' to 600' above the valley floor. Rough and Ready lies near a tributary 2 miles northeast of Squirrel Creek and 300 feet above Penn Valley. Groups

of hills constitute low parallel ridges, ascending eastward to the Grass Valley plateau, about 2500' above sea level. The north side of the

Rough and Ready divide is drained by Deer Creek, north of which the ground rises to a series of parallel hilltops, the highest of which is about 700 feet above the creek.

In the southwest portion of the district, south of Perin Valley, Indian Springs plateau extends eastward from Indian Springs Hill. The

elevation of this platenu averages 1800'. I t is drained on the north by Clear Creek, which flows northwest to join Squirrel Creek. East

of the plateau the surface is mnde irrrmi1:ir hy a nlinlber of low hills.

Geology.

There is one small area of slates and cluartzites of the Calaveras formation in the nortileast corner of the district, being continuous with those formations of the Grass Valley region to the ~011th. The region is composed chiefly of igneous rock. The tlirre most extensive forma- tions are granodiorite. gablwo-diorite. irntl ~~rnphibolitc. oc.crlrring from west to east in the order mentionctl. To the west tile granodiorite is

in contact with diabnse; i t occurs in and north of Penn Valley about Anthony House and a t Rapps Ranch. I t also occurs north of Rough and Ready. in Deer Creek Caiion. Kentucky ravine and on the inter- vening divide. Sorn~what over a mile east of Rapps Ranch a body of gabbro-diorite, one mile in greatest width and four miles lonq, grades into the snrrounding granodiorite. Soutl~west of R o n ~ h and Ready is a large body of gabbro-diorite, two miles in greatest width, in contact on the west with nranodiorite and on tlrc enst with nrnphibolite. (;ilbhro- diorite forms the sorithern end of n large nren of granodiorite enclosed in the main cliabase area in the northwestern pnrt of the Srnartsville qiiadrangle. Frequent transitions from grnnodiorite into adjoining gabbro-diorite are found. showing that the latter is probably a magmatic segregation.

Amphibolite is in contact with g~ilhro-diortte both rust and soutli of Rough and Ready. I t is macsive and is tkotlght to have been derived from gabbro-diorite. The texture is not the same throughout the area, ~ n d masses of diorite and grthbro are often included. The change to amphibolite is brought about by pressure, which changes the pyroxene to green uralitic hornblende. When the change is complete the amphib- elite is composed of secondary nmphihol, ~ l h i t e , cpidote, chlorite and other minerals. The amphibolite belt has R width ranging from 2 miles