STATE OF CALIFORNIA EARL WARREN, Governor DEPARTMENT OF NATURAL RESOURCES WARREN T. HANNUM, Director DIVISION OF MINES FERRY BUILDING. SAN FRANCISCO 11 OLAF P. JENKINS. Chief SAN FRANCISCO SPECIAL REPORT 28 DECEMBER 1952 GEOLOGY OF THE MAMMOTH MINE SHASTA COUNTY, CALIFORNIA By A. R. KINKEL JR. and WAYNE E. HALL Prepared in cooperation with the United States Geological Survey 40' 30 ..OUNTAfe^D-Vrf: WWW Q U ADfc ANGLEVV-AY/* W\WW\\\ ^"^XT/fe^C \\\W\W*A-*y£'' A fv^S MASSIVE SULFIDE MINES SUTRO STAUFFER GOLINSKY MAMMOTH UNCLE SAM EARLY BIRD SHASTA KING .BALAKLALA KEYSTONE SPREAD EAGLE STOWELL SUGAR LOAF LONE STAR IRON MOUNTAIN EXPLANATION Biotite-quartz diorite .^-'-Av Albite granite Sedimentary rocks < Balaklala rhyolite Copley greenstone 1 2 2° 30 Figure 1. Index map showing location and geologic setting of the Mammoth mine, Shasta County, California. GEOLOGY OF THE MAMMOTH MINE, SHASTA COUNTY, CALIFORNIA * By A. R. Kinkel, Jr.,*» and Wayne E. Hall •• OUTLINE OF REPORT lite, the upper unit of the Halaklala rhyolite. In detail, ore is present Page where gently dipping bedding-plane foliation, which is localized by Abstract 3 layers of pyroclastic material, is intersected by steep fracture cleav- Introduction 'A age. The solutions were introduced into this structure by premineral History, production, and grade 4 faults that apparently acted as feeder fissures. Regional geology 4 Geology of the mine area 5 INTRODUCTION Formations 5 Structure 7 Previous Work. Geologic studies of the copper- and Ore deposits ______ 11 zinc-bearing areas of Shasta County have been carried on ( haracter and distribution 11 • , ... ,, n t_-'i, , ■ • .i • _• Hypogene minerals _ 12 intermittently tor many years; Diller s work in this dis- Oxidation and enrichment 13 trict, beginning in 1884 and culminating in his report on Pangenesis 13 the Redding quadrangle in 1906 1 has been of inestimable Ore'ooli.roi's' 1 olteration " he, P to the authors. More recent work on the base metal References r __ S _ 15 deposits includes that of Graton 2 , Seager 3 , Kinkel and Hall 4 and Kinkel and Albers 5 . This report is the first Illustrations published description of the ore deposits of the Mammoth Figure 1. Index map showing location and geologic setting of mine, which is one of the largest mines in the West Shasta the Mammoth mine, Shasta County. ------ 2 copper-zinc district. The work is part of a cooperative Z. Photo showing view east from Mammoth mine 4 , _i tt «__'_■ i __ - . :.. Photo showing Mammoth mine; view west from road 5 program between the IT. S. Geological Survey and the 4. Photo showing volcanic breccia horizon in the coarse- California Division of Mines for studying the ore deposits phenocryst rhyolite .__ s of the Shasta copper-zinc district ; the field work was done 5. Diagram showing relationship between bedding-plane during August and September 1950 foliation, fracture cleavage, and ore zones of Mam- m , __ . . ' ' »_»■,-. moth mine, Shasta County 9 * he Mammoth mine is 13 miles northwest of Redding, Plate l. Composite plan of underground workings, Shasta County, California, in sec. 32, T. 34 N., R. 5 W., Mammoth mine, Shasta County In pocket Mount Diablo base and meridian. The principal workings 2. Geologic map of Mammoth mine, Shasta are at an elevation of about 3,000 feet in the rugged foot- 3. GeSScVctious; vZZri^^to^^* ** hi,ls ? f u the u Klamath Mountains (fig. 1). The mine is County In pocket owned by the United States Smelting Refining and 4. Plan of 200-foot level, Mammoth mine In pocket Mining Co. During mining operations from 1905 to 1925 5. Plan of 300-foot level, Mammoth mine__ __In pocket the mine was accessible by road from Redding, but the 6. Plan of 470-foot level, Mammoth mine In pocket fl«„,q; e ou„ *- t i • in__ _. j _i_ i 7. Plan of 500- and 540-foot levels. Mammoth flooding of Shasta Lake in 1944 submerged the lower part mine In pocket of the road. The road from the lake to the mine is 3 miles 8. Plan of 670-foot level, Mammoth mine In pocket long and climbs 2,000 feet in elevation (fig. 1). In 1950 it 9. Structure contour map on the base of the was not pasS able for a car because of minor washouts. The coarse-phenoeryst rhyolite, Mammoth mine In pocket __j i-„* j • -moc v. __. i j mine plant was removed in 1925, when the mine was closed ; ABSTRACT an > nc ^ ne d tramway that carried the ore to a railroad spur on the North Pork of Backbone Creek has also been re- The Mammoth mine is in the West Shasta copper-zinc district 13 moved. Figure 3 is the view west from the road to the miles northwest of Redding, California, in the foothills of the Mammoth mine, ill 1950. Klamath Mountains of northern t alifornia. It is at an elevation of ' 3,000 feet. It is not accessible by road (1951) because the recent Acknowledgments. This report and the accompanying flooding of Shasta Lake has covered parts of the old access roads. maps were pre p a red by combining the surface geologic The ore produced from the Mammoth mine during its period of mapping done by A. R. Kinkel, Jr. and Wayne E. Hall operation from 1905 to 1925 amounted to 3,395,145 tons. Of this, e \i tt o n i ■ i o •__. _u j j 3,311,145 tons was direct-smelting copper ore, and 84,000 tons was of the U - S - Geological Survey with the underground high-grade zilc ore. The average grade of the ore was 3.95 percent geologic information supplied by the United States Smelt- copper, 4.62 percent zinc, 0.039 ounce of gold, and 2.32 ounces of ing Refining and Mining Co., owners of the Mammoth silver per ton. mine. Geologic maps of the mine workings and the pro- The ore occurs as large, flat-lying tabular bodies of massive pyrite duction data were supplied by R. N. Hunt, Chief Geolo- that contain copper and zinc, and minor amounts of gold and silver. . . „ ,, TT ., , m, : m ,.• t> r • i -n/r- • The ore is a replacement of Balaklala rhyolite and formed near the gist of the United States Smelting Refining and Mining contact between the upper two of the three units in the Balakala Co., who also supplied records of the drilling and fur- rhyolite. The upper unit is a thick, massive rhyolite with coarse nished information on the geology in the underground phenocrysts of quartz and feldspar, and the middle unit consists of workings. In addition, Ralph Tuck, geologist for the rhyolite flows and rhyohtic pyroclastics with much smaller pheno- T _ . , -.. <-■ ,,• t» j> • V -»*-■ • r-i _ crysts. Some bedded tuff is present adjacent to the contact between United States Smelting Refining and Mining Co., spent the two units and immediately over the ore bodies. Individual ore 4 days in the field with the authors and contributed many bodies reach maximum horizontal dimensions of 900 feet by 500 feet and a maximum thickness of 110 feet. The ore zone has a known ' D1 " er -, J « s - ?*?" iption , ,° s f ^J 1 * Re , d , d „ , ? B - ^V^,?" 11 ^ 430 ' p , p - Jl; 1 - 1 ^' ?,^i_ r,ivi,i,,n n f mi^ __. u- i _ _ i m_ -l - » Seager, G. F., Unpublished report of the (.alifornia Division of Mines, graphic and structural. The ore zone occurs along the crest of an » Kinkel, A. R., Jr., and Hall, W. E., Geology of the Shasta King mine, elongated domelike arch at the base of the coarse-phenocryst rhyo- Shasta County, California: California Div. Mines Special Rept. lb, 11pp., 1951. •Publication authorized by the Director, U. S. Geological Survey; 5 Kinkel, A. R., Jr., and Albers, J. P., Geology of the massive sulfide manuscript received for publication June 17, 1952. deposits at Iron Mountain, Shasta County, California: California " Geologist, U. S. Geological Survey. Div. Mines Special Rept. 14, 19 pp., 1951. (3) Special Report 28 n *Jr£.2s^ Figure 2. View east from the Mammoth mine. useful suggestions. R. T. Walker, a geologist for the com- pany during part of the mining operations, has con- tributed valuable information on the appearance and occurrence of the ore. As many of the workings in the vicinity of the ore bodies and all of the stopes were inac- cessible at the time of the authors' study, no underground mapping was done by the authors. HISTORY, PRODUCTION, AND GRADE The date of discovery of the Mammoth mine is known only to have been after 1880 and probably before 1890. George Graves is reported to have discovered the ore body, and prior to 1900 a Mr. Nelson worked the property in a small way to recover the gold from the gossan. The United States Smelting Refining and Mining Co. acquired the property in 1904, and began large-scale mining opera- tions in 1905. The mine was operated continuously from 1905 to 1919 but was closed from 1919 to late 1923. Opera- tions were resumed late in 1923 but were again suspended in 1925. No ore has been mined since 1925, although some exploration work has been done. Plate 1 shows the extent of the mine workings. The United States Smelting Refining and Mining Co. erected a smelter in 1905 on the Sacramento River, \\ miles from Kennett. The smelter contained three blast furnaces, and two additional blast furnaces were built in 1907. The smelter was dismantled in 1925, and the smelter site now lies beneath Shasta Lake. Zinc was not recovered from the direct smelted ore or from the slag, and the sulfur dioxide in the fumes was not utilized. Two kinds of ore have been mined from the Mammoth ore bodies. Most of the ore was mined only for its copper and minor gold content and was direct-smelted. Some bodies that contained high percentages of zinc, however, were mined as zinc ore during World War I, when the price of spelter was sufficiently high to justify shipping the ore to refineries in the Midwest. Table 1 gives the production of copper and zinc ore from the Mammoth mine from 1905 to 1925. The gross value of the recovered gold, silver, and copper in the copper ore was $51,970,290, and the value of the zinc in the zinc ore was $4,525,870. REGIONAL GEOLOGY The oldest formation exposed in the West Shasta copper-zinc district is the Copley greenstorle of probable Middle Devonian age (fig. 1). It is composed primarily of andesitic flows and pyroclastic rocks. The Balaklala rhyolite of Middle Devonian age overlies the Copley con formably. The rhyolites and associated tuffs and rhyolitic pyroclastics form a broad, elongate, complex volcanic pile, probably with many centers of volcanic activity. The Balaklala is conformably overlain by shale, tuff, and lime- stone of the Kennett formation of Middle Devonian age The Kennett is overlain, with apparent conformity in the area mapped, by shale and conglomerate of the Bragdon formation of Mississippian age. The Paleozoic rocks are intruded by a pluton of albite granite and another of biotite-quartz diorite. The albite granite is probably contemporaneous with a Late Jurassic KD be 01 Mammoth Mine, Shasta County -«*?. $M i Figure 3. Mammoth mine ; view west from the road to the mine orogeny, but the biotite-quartz diorite, although it is also probably of Late Jurassic age, was emplaced after the orogeny. A preliminary geologic column for the West Shasta copper-zinc district is given in table 2. The Paleozoic rocks in the West Shasta copper-zinc district have been folded into a broad arch with an axis trending N. 15° E. that passes through Iron Mountain and Behemotosh Mountain. Dips on the flanks of the fold are mostly 10 to 20 degrees, but locally they may be vertical. The broad arch has a culmination in the central part of the mining district at the Uncle Sam mine, and plunges gently to the north in the northern part of the district, north of the Mammoth mine. The arch is broken by numerous faults. Two directions of faults are promi- nent ; one set strikes about N. 30° W., and the other set strikes N. 60°-70° E. Both vertical and horizontal move- ments are recognized ; in nearly all the faults the north block is the downthrown side. GEOLOGY OF THE MINE AREA Formation* Only the Kennett formation and the Balaklala rhyolite crop out in the vicinity of the Mammoth mine (pi. 2). Balaklala Rhyolite. The Balaklala rhyolite consists of porphyritic and nonporphyritic rhyolite flows with inter- calated coarse to fine rhyolite pyroclastics. Although the formation consists mainly of flows and pyroclastics, dikes and sills of rhyolite intrude the volcanic pile and the underlying Copley greenstone. Individual flows and pyroclastic beds are lenticular, and few can be traced for as much as 2,000 feet. The most notable exception is the broad, elongate mass of coarse-phenocryst flow rhyo- lite and associated tuffs, which forms the upper unit of the Balaklala and extends from the Stowell mine to the Golinsky mine, except where cut out by the major canyons — a distance of approximately 6 miles. Although no flows or pyroclastics are continuous throughout the Balaklala rhyolite, and no horizon marker is present, a general stratigraphy is recognized in the volcanic pile. The Balaklala is divided into three main units as shown in table 3. The table contains a preliminary generalized stratigraphic section of the Balaklala that has been built up from studies of the district. The lower unit of the Balaklala rhyolite is the most extensive and most continuous. It consists mostly of light- gray to light-green nonporphyritic rhyolite and rhyolite tuff and volcanic breccia, but locally it contains a few flows of porphyritic rhyolite and beds of pyroclastics. Much of the rhyolite is flow-banded, and amygdaloidal rhyolite is fairly common. It contains a few thin mafic flows near the base similar to the underlying Copley greenstone. This lower unit of the Balaklala is as much as 900 feet thick at some places, but its thickness has a wide range. Most of the lower unit of the Balaklala is present in the area of the Mammoth mine and is exposed in the deep canyon of Little Backbone Creek north of the mine. The middle unit of the Balaklala consists mainly of light-green to light-gray porphyritic rhyolite flows and pyroclastics with 1- to 4-mm phenocrysts of quartz and feldspar ; it also contains a few flows of nonporphyritic Special Report 28 Table 1. Annual production of ore from the Mammoth mine, 1905-25 Year Ore (tons) Gold (ounces) Silver (ounces) Copper (percent) Zinc (percent) Insoluble (percent) Iron (percent) Sulfur (percent) 1905. .- -. 13.868 181,733 201,124 311,997 370,985 315.189 269,438 273,555 269,233 227.459 242,573 223,458 147,340 76,079 37,733 9,221 115,814 34,346 0.029 0.048 0.039 0.033 0.036 0.038 0.032 0.034 0.036 0.043 O.038 0.042 0.040 0.040 0.040 0.050 0.045 0.037 Coppi 1.94 2.12 1.94 1.90 2.13 2.38 2.26 2.24 2.19 2.28 2.21 2.74 2.46 2.29 2.50 2.85 2.39 2.17 jr ore 4.30 3.95 4.15 4.03 4.15 3.83 4.06 3.47 3.58 3.96 3.75 4.77 4.22 3.91 4.10 4.42 4.27 4.34 1906 3.30 4.70 4.70 4.70 4.40 4.20 4.20 3.80 4.10 3.80 4.20 3.80 4.30 3.70 5.00 3.70 4.30 9.5 7.7 12.6 13.2 15.1 12.4 12.6 14.9 12.5 12.8 13.8 20.4 14.2 14.4 16.6 13.5 11.0 39.0 38.4 35.6 34.9 34.2 35.4 34.0 32.7 33.9 33.3 32.6 31.4 32.4 32.9 33.2 35.2 36.6 42 2 1907 44.5 1908 41.9 1909 42.0 1910 40.7 1911.- 44.7 1912. 40.9 1913... 39.8 1914 40.3 1915. 40.0 1916 . 37.6 1917.. 36.6 1818.. 37.6 1919... _ 37.8 1923 36.9 1924 1925 40.2 41.4 Total and weighted averages 3.311,145 0.038 2.24 3.99 4.20 13.3 34.3 40.4 1914-1915 84.000 0.078 Zin 5.79 : ore 2.40 21.10 3,395.145 0.039 2.32 3.95 4.62 Published by permission of the United States Smelting Refining and Mining Co. Table 2. Preliminary geologic column of the West Shasta copper-zinc district, Shasta County, California. Age Formation Thickness (feet) Lithology Recent Alluvium 0-150 Alluvium, landslide deposits. Pleistocene Red Bluff fo; -nation* 0-100 Cemented sand and gravel. Cretaceous Chico formation* 0-200 Cemented mudstone, sand, and gravel. Late Jurassic Rocks of the Shasta Bally batholith Biotite-quartz diorite. Jurassic(?) Rocks of the Mule Mountain stock Albite granite. Mississippian Bragdon formation* 5,000-6,000(?) Shale, sandstone, conglomerate. Middle Devonian Kennett formation* 0-865 (T) limestone, dark-gray shale, black cherty shale, tuff. Middle Devonian Balaklala rhyolite 0-3,500 Soda rhyolite, quartz porphyry, pyroclastics. Middle Devonian(?) Copley greenstone 3.500 Greenstone flows and pyroclastics, diabase, andesite. • These formations are largely eroded In the central part of the mining district. Mammoth Mine, Shasta County Table S. Generalized stratigraphy of the lialaklala rhyolite. Unit Description Thickness (feet) Upper "nit Tuff with some quartz phenocrysts more than 4 mm in diameter, interbedded with thin shale beds. Transitional to Kennett formation. Coarse-phenocryst rhyolite with quartz and feldspar phenocrysts more than 4 mm in diameter. Sporadic tuff and volcanic breccia at the base of the unit. 0-300 0-1,200 0-150 Middle unit Volcanic breccia and tuff, and medium-phenocryst rhyolite flows with quartz and feldspar phenocrysts 1 to 4 mm in diameter. Medium- phenocryst rhyolite flows and minor pyroclastics. Minor flows of nonporphyritic rhyolite. 0-800(?) 0-600(?) (except for one area of unusu- ally large thickness) Lower unit Nonporphyritic rhyolite, much rhyolitic pyroclastics, and flow-banded and amygdaloidal rhyolite. Includes a few thin flows of medium-phenocryst rhyolite and a few thin mafic flows near the base. 0-900(7) Transition zone to un- derlying Copley greenstone. Mixed, mafic and silicic pyroclastics. 0-150 rhyolite. The upper part of the middle unit of the Balak- lala contains abundant, although discontinuous, coarse and fine pyroclastics interlayered with or overlying the medium-phenocryst rhyolite. The upper part of the mid- dle unit is the ore horizon, and the ore deposits, as far as is known, occur as replacement bodies in medium- phenocryst rhyolite flows that lie under beds of pyro- clastics. The middle unit does not extend as far laterally as the lower unit, but it is more extensive than the upper unit of the Balaklala rhyolite. It ranges from a few feet to 600 feet in thickness, but its thickness varies greatly in short distances because of the piling up or absence of individual flows. At the Mammoth mine, the thickness of this unit ranges from about 150 to about 300 feet, but the base of the unit is very irregular. The upper unit of the Balaklala rhyolite consists of coarsely porphyritic rhyolite with quartz and feldspar phenocrysts that are more than 4 mm in diameter. It is about 1,200 feet thick at Mammoth Butte (fi<*. 1) but thins rapidly in all directions therefrom. A thin bed of tuff or volcanic breccia is present at many localities at the base of the coarse-phenocryst rhyolite. This pyro- clastic bed is generally 10 to 50 feet thick, but where it is composed mainly of volcanic breccia it reaches 150 feet in thickness. Tuff beds are also present over the coarse- phenocryst rhyolite and are interbedded with thin shale beds of the overlying Kennett formation. The origin of the coarse-phenocryst rhyolite is of in- terest, as this rock is the "cap rock" for ore bodies; that is, all known ore occurs at or a short distance below the lower contact of the coarse-phenocryst rhyolite. Although some geologists have considered the coarse- phenocryst rhyolite to be a sill or gently domed laccolith, the present authors contend that the layers of pyroclastic material (interpreted by them as volcanic breccia and bedded tuffs containing fragments of coarse-phenocryst rhyolite, fig. 4) are evidence of surface origin; and that the coarse-phenocryst rhyolite was extruded as a surface flow, forming a broad, low domelike mass, the thickest part of which was at the principal vent at the Uncle Sam mine. In addition, the interbedding between the coarse- phenocryst rhyolite tuff and volcanic breccia at the top of the Balaklala rhyolite and the shaly tuff and shale at the base of the overlying Kennett formation is evidence of a sedimentary sequence. Kennett Formation. A small area of the Kennett formation of Middle Devonian age is exposed in the south- east corner of the mapped area. It is an extensive forma- tion to the east and northeast of the mine and probably once covered much of the mapped area. It lies conform- ably on the Balaklala rhyolite and dips gently to the east. The lower part of the Kennett consists of gray shale inter- bedded with water-laid rhyolitic tuff and arkose typical of the Balaklala. Structure The Mammoth mine lies along the crest of a broad arch or elongated domelike structure in the enclosing rocks. The rocks in the mine area are gently folded, and several small flexures are present in addition to the broad arch. Indi- vidual ore bodies are located in part along minor flexures on the major arch. Some of the rocks have been sheared and contain oriented mineral grains, which are commonly restricted to bands in the rock. The degree of foliation is dependent mainly on the competence of the various units. The folding and the foliation are interrelated elements in the geologic structure, and they are of equal impor- tance in the localization of ore. The folds, which are revealed by the bedding of tuffs and volcanic breccia, are shown on the level maps (pis. 4-8) and on the structure contour map (pi. 9). The relationship between foliation and bedding is shown on plate 2 and figure 5. Several strong fault zones and many weak ones cut the rocks in the mine area. Most of these are probably postmineral in age, but a few that are premineral in age probably were feeder channels for mineral-depositing solutions. Folds. The bedding in the mine area is delineated by the contact between the overlying coarse-phenocryst rhyo- lite and the underlying medium-phenocryst rhyolite and nonporphyritic rhyolite, and by bedded material between these two units of the Balaklala rhyolite. The structure contour map (pi. 9) shows that a slightly elongate domelike structure trends N. 45° E. and has a culmination in the central part of the group of ore bodies. There are also numerous smaller arches or elongated con- tour "highs," the alinements of which appear to have no relation to the alinement of the main dome. Local dome and basin structures occur at the base of the coarse- phenocryst rhyolite throughout the district, and these range from small rolls a few tens of feet across to struc- tures that are measured in thousands of feet. Special Rkport 28 ■St'* t<$$F Figure 4. Volcanic breccia horizon in the coarse-phenoeryst rhyolite. The sedimentary material, where it is present at the base of the eoarse-phenocryst rhyolite, is useful in de- lineating folded structures. This material was not seen underground by the authors, but on the basis of surface exposures it is thought to be a tuff. Dips and strikes in the bedded material underground, taken by company geologists, show that in most places the bedding is parallel to the contact of the coarse-phenoeryst rhyolite (pis. 3, 5, 6, 7). Some random orientation of bedding has been observed, but such variations may be caused by close folding, faulting, or minor intrusions of coarse-pheno- eryst rhyolite. If it were not for the presence of water-laid, bedded tuffs at the base of the coarse-phenoeryst rhyolite, it might be argued that the present relief at the base of this formation was a result of the irregular topography of the old land surface at the time of extrusion of the formation, rather than of folding. The old surface prob- ably had considerable relief, caused by the uneven dis- tribution of the older volcanic flows and local eruptions of volcanic breccia. The distribution of the bedded tuff, however, would be more even and widespread than it is, even if tuff was erupted below water level, unless some of it was removed from higher parts of the surface by erosion and redeposited in local basins. The bedding in the tuff is conformable with the overlying flow contacts. Also, the greatest thickness of the bedded tuff at the bast of the coarse-phenoeryst rhyolite in the Mammoth mint occurs along the crests of the arches (300-, 470-, and 500 foot levels) and tuff is absent at most places along th< flanks of the arches. Thus it seems certain that, althougl some relief in the surface of deposition can be assumed the structures shown on the structure contour map an secondary features that have resulted chiefly from fold ing. Flexural-slip folding, that is, folding in which move ment along bedding planes is concentrated in the incom petent layers, and platy minerals in these layers are ori ented parallel to bedding (Swanson, 1941, p. 1256; Knop and Ingerson, 1938, pp. 157-161), is locally well develops in the West Shasta copper-zinc district. It occurs in con junction with poorly developed fracture cleavage in th competent layers. At the Mammoth mine the degree an< type of foliation that is developed depend on the eomp€ tence of the rock units. The nonporphyritic rhyolite ani the medium-phenoeryst rhyolite are competent rocks. Th beds of pyroclastics at the base of the coarse-phenocrys rhyolite form an incompetent layer that has a considei able areal extent ; the coarse-phenoeryst rhyolite is i thick, massive, very competent layer. During the foldin in the mine area, steep fracture cleavage — with som recrystallization and alinement of minerals parallel t Mammoth Mine, Shasta County EXPLANATION £ 53 ■c c Q. O a | St, cj c: o i; Medium -phenocryst rhyc nonporphyritic rhyolite 1 t, tuff and volcanic bre /\A I II 9|||0Al|J D|D|)(D|Da 03 as ■a m o a a 03 i in Special Report 28 Table {. Production and grade of slopes and other ore blocks of the Mammoth mine | Copper ore Ore body Tons Gold (ounces) Silver (ounces) Copper (percent) Zinc (percent) Lead (percent) Iron (percent) Sulfur (percent) Insoluble (percent) 10,000 65,000 15,000 1,970,145 300.000 2.000 100.000 2.000 385,000 200,000 100,000 2.000 100.000 60.000 0.10 0.04 0.04 0.03 0.04 0.03 0.04 0.03 0.04 0.04 0.04 0.03 0.04 0.04 15.0 7.0 2.0 1.8 2.2 2.0 2.2 2.0 3.0 3.0 3.0 2.0 3.0 3.0 0.5 10.0 4.0 3.8 3.8 3.0 3.8 3.0 4.5 4.5 4.5 3.5 5.0 6.0 ' Clark - .- - .. Metralf 2784 Fridav Lowden . _ . Zinc ore Tons mined (before sorting) Grade of sorted ore* Gold (ounces) Silver (ounces) Copper (percent) Zinc (percent) Lead (percent) Iron (percent) Sulfur (percent) Insoluble (percent) Yolo . 58,000 Not available 16,000 5.000 2.500 Not available 0.12 0.02 0.13 0.40 Grade of 5.44 1.40 6.50 4.90 insorted ore 2.20 1.80 1.00 0.72 * 36.20 33.30 27.70 36.35 3.00 nil 1.00 1.40 10. 1 9.2 9.5 25.2 24.7 23.5 20.7 19 8 31.8 Metralf Total* 84,000 0.078 5.79 2.40 21.10 12.6 Sec table 5. Pyritic ore underlying copper ore bodies 0.04 0.03 0.03 0.01 0.03 0.04 0.01 0.05 1.0 0.4 0.2 0.6 10 1 .1 0.3 1.1 2 0.5 0.5 0.5 1.2 2.2 0.5 2 42.0 38.0 43.0 45 40.0 45.0 35.0 40.0 45.0 40.0 40.0 10 18.0 10.0 Clark rrmay Lowden I 313, at 390-foot level Total ... . 0.028 0.56 0.9 41 4 t Published by permission of the I'nlted States Smelting, Refining and Muting Co. cleavage planes — developed in the non-porphyritic and medium-phenoeryst rhyolite, particularly near (he axes of folds. Movement along the bedding plane, with accom- panying foliation parallel to the bedding plane, was con- centrated in the layers of pyroclastics at the base of the coarse-phenocryst rhyolite (fig. 5). In the overlying massive coarse-phenocryst rhyolite, foliation is locally present but is rare because of the great thickness and competence of this rock. Faults. Several large fault zones and many small faults are shown on the maps of the mine levels. They are of several ages, as shown by one fault cutting another; most are probably postmineral in anly 5 to 10 feet on either side of the fault. The California fault is probably a premineral fault ; •easons for this view are given under Ore Controls. That jostmineral movement has also occurred on this fault is shown by offset ore bodies. The north block moved east ind down, but the exact amount of movement is not mown. The ore bodies plunge at a low angle to the south- vest along the fault, so that the present position of offset segments of ore bodies could be due either to mainly dip- ilip or mainly strike-slip movement. The 313 fault and he 12-drift fault on the 200-foot level (pi. 4) appear to >e offset about 250 feet horizontally by the California 'ault, although neither the dips nor the accurate locations »f these faults are known where they are cut by the Cali- fornia fault. If the Main and Winslow ore bodies were >ne ore body before being cut by the California fault, in apparently reasonable assumption, then the dip-slip novement on the fault would be less than the strike-slip novement. Along some parts of the California fault the ower contact of the coarse-phenocryst rhyolite has a rery low dip, and measurements of the elevation of this contact on either side of the fault indicate a vertical lisplacement of 130 feet. From available data, the strike- lip displacement appears to be about twice the dip-slip lisplacement. The 12-drift fault and the 313 fault, with its probable xtension as the Yolo (313) fault, are shown on the maps •f the mine levels, (pis. 4-8) and the cross sections (pi. 3). The vertical offset on each of these faults is approxi- nately 40 feet, and the north side is down relative to he south side ; but nothing is known about a possible lorizontal offset on these faults. They are older than the California fault and are offset by it. The Schoolhouse fault is exposed only on the 670-foot evel (pi. 8) and for a short distance on the surface. The ipproximate vertical offset of the base of the coarse- )henocryst rhyolite at the surface is about 100 feet, and he north side is down relative to the south side ; but xposures are poor where the fault cuts this contact. The iffset on the Schoolhouse fault appears to be less in the ast end of the mapped area than in the west end. The hyolite along the Schoolhouse fault at the surface is >yritized and altered to clay minerals. The Gossan fault is exposed on the 670-foot level (pi. 8) and for a short distance on the surface. The rocks on the cast side of the fault are dropped relative to those on the west side ; on the basis of a doubtful correlation of rock types, the vertical offset is judged to be about 50 feet. The rhyolite is pyritized and altered to clay along the outcrop of this fault. Several north-dipping faults that strike N. 60°-80° W. are known in the vicinity of the Friday Lowden and Hanley ore bodies at the southwest end of the mine. The Friday fault is one of this group of faults that cut the Friday Lowden ore body and may offset it. The total offset on this group of faults may be considerable, but no data are available. The Clark fault is a minor fault with a 10- to 20-foot offset. The north side has moved down relative to the south side (pi. 3, section D-E-F-G). Ore Deposits Character and Distribution The ore bodies of the Mammo+h mine are large, flat- lying, tabular bodies of copper- and zinc-bearing pyritic ore. The known ore bodies extend along a horizontal distance of 4,200 feet ; but the northeast end of the ore zone has been eroded, and exploration has not delimited the southwesterly extension of the zone. The central part of the ore zone has a width of 1,000 feet. Minable ore bodies occur throughout the ore zone, but the entire zone is not ore. Individual stopes reach a maximum horizontal dimension of 900 feet by 500 feet and the maximum thick- ness of ore is 110 feet ; ore bodies range from these maxima down to small stopes from which only a few hundreds of tons were mined. The ore zone lies along the crest of a broad arch in the rocks, and all known ore occurs at or a short distance below the contact between the coarse- phenocryst rhyolite and the underlying rhyolitic tuff and flows (pi. 3). The ore is formed by replacement of Balaklala rhyolite. Table 4 gives the production and grade of stopes and other ore blocks; it also shows the uniformity of the gold, silver, and copper content of all the copper ore bodies, and the sharp distinction between copper-rich ore and zinc- rich ore. The pyritic ore that underlies the copper ore bodies contains a smaller quantity of copper than the massive sulfide that was mined for its copper content, but it is the same type of ore. Table 5 gives information that is not available elsewhere on the distribution of metals in the zinc-rich parts of the ore bodies. The grade of the material .sorted from the high-zinc part of the ore was calculated from the known assays. It is apparent, for instance, that the material Table 5. Results of hand sorting of zinc ore from the Mammoth mine. (Tons) Gold (ounces) Silver (ounces) Copper (percent) Zinc (percent) Iron (percent) Insoluble (percent) ; rude ore produced*. orted ore shipped ercent increase or decrease, rade of discard (calculated) See table 4. 84,000 28.800 —65.7 55,200 0.078 0.111 +42.3 0.061 5.79 9.51 + 63.6 3.82 2.40 2.4 0.0 2.4 21.10 39.6 + 87.5 11.42 12.6 8.9 -29.4 14.5 35.5 16.8 -52.6 45.3 12 Special Report 28 sorted from the zinc ore was rock that contained some copper, gold, silver, zinc, and iron, but contained more rock material than massive sulfide ore (45.3 percent in- soluble). The figures suggest that the discarded material consisted of rock containing stringers of the massive sulfide type of ore in essentially unmineralized rock, rather than that the discarded material contained dis- seminated minerals. Little information is available to the authors on the appearance of the ore underground, or on the nature of the contact between ore and waste. The appearance of the specimens that the authors have collected from dumps and along the tramline, and the higher content of in- soluble material in analyses of ore, show that although most of the ore was massive and pyritic, it contained more quartz and altered, unreplaced rock material than the ore of the Iron Mountain and Shasta King mines. However, observers who have seen the ore underground have noted that quartz is rarely visible megascopically in the Mammoth mine ore except where a few late veinlets cut both the ore and the wall rocks. Frozen contacts between ore and wall rocks are re- ported to be rare ; at most contacts, as in the other mines in the district, ore is separated from rhyolite by a clay selvage. R. N. Hunt 7 states that some ore bodies had sharp, smooth outlines. In these ore bodies the contacts between massive sulfide ore and wall rock were sharp; the ore was separated from the wall rock by a thin selvage of gouge at the ends of ore bodies, as well as along the top and bottom of the ore body, and the wall rock con- tained little or no pyrite. Contacts of this type are similar to those at Iron Mountain and at the Shasta King mine. R. T. Walker 8 , however, reports that the material be- tween some of the stopes was massive sulfide containing less copper than the ore that was mined. The ore zone was continuous between these stopes, and some stope outlines mark only the economic limit of mining. Thus, although many stopes were mined to a sharp waste wall at the ends of the ore bodies, at some places an individual stope does not represent the extent or continuity of a body of massive sulfide, which may be of considerably greater extent than is indicated by the outline of the stope. The ore zone at the Mammoth mine extends S. 70° W. for 3,000 feet from the outcrop of the Main ore body to the deepest exploration southwest of the Friday Lowden ore body. The general trend of individual ore bodies — and of the ore zone as a whole, if the Gossan ore body is included — is more nearly S. 60° W. Part of the ore zone is eroded between the Gossan ore body and the Main ore body. Although the Gossan ore body lies at a lower strati- graphic horizon than the main part of the ore zone, it seems reasonable to assume that ore bodies were present along the eroded upper part of the ore zone and in the eroded extension of the ore zone northwest of the Gossan ore body. The ore zone must thus have been at least 4,200 feet long, and it may have been considerably longer. The plunge of the ore zone ranges from horizontal to vertical, but from the outcrop of the Main ore body to the deepest known ore the plunge averages only 14° W. A few large faults and many small faults cut the ore bodies. Small faults are marked in the ore by slickensided surfaces, and small offsets complicated stope layouts in 7 Oral communication. 6 Oral communication. some places. The larger faults appear to have offset ore bodies several hundred feet and the present distribution of ore bodies is due in part to postmineral faulting. The alinement of zinc-rich ore along the 313 fault and the Yolo (313) fault is discussed under Ore Controls. Hypogene Minerals The mineralogy of the primary ore from the Mammoth mine is comparatively simple. The ore consists mainly of pyrite, chalcopyrite, and sphalerite ; minor galena and tetrahedrite are present, and the gangue consists of seri- cite, hydromica, chlorite, quartz, and calcite. Graton (1909, p. 102) reports finding also small particles of i barite in the gossan and in the sulfide ore, but this mineral was not observed by the authors. The ore contains small quantities of gold and silver, but no gold or silver min- erals have been recognized. Sulfide minerals constitute about 85 percent of the ore. Pyrite. Pyrite is the most abundant mineral in the primary ore and constitutes about 70 percent of the ore | by volume, except in the zinc-rich ore bodies. The range in pyrite content is from 85 percent in the low-grade copper or pyritic ore bodies to a few percent in the high grade zinc ore bodies. In the low-grade pyritic ore, pyrite megascopically appears to form massive aggregates wit! a few disseminated 1- to 2-mm euhedral cubes and pyrito hedrons. Under the microscope pyrite is seen most com monly as discrete subhedral grains that average 0.4 mm in diameter, separated by a network, 0.05 to 0.3 mm thick of gangue and/or chalcopyrite and sphalerite, but hi places the pyrite forms granular aggregates without th< surrounding network. Chalcopyrite. Chalcopyrite constitutes from 1 percen of the low-grade pyritic ore to more than 50 percent o the high-grade ore, and it averaged 12 percent in the or that has been shipped. It is present as a network patten around grains of pyrite, as thin veinlets cutting pyrite as minute blebs and corroded relicts in sphalerite, and a bands and irregular masses associated with sphalerite. Chalcopyrite, sphalerite, and quartz commonly f orrr I a network, generally less than 0.3 mm thick, around pyritil grains. The sulfide mineral grains are so small that 1 1 the unaided eye they appear to blend as massive sulfid with a metallic luster and a brassy yellow color betweei that of pyrite and chalcopyrite. Pyrite has a uniforr distribution throughout the copper ore, indicating tha the chalcopyrite network did not have a very corrosivi effect upon pyrite. In only one of the polished section studied had chalcopyrite corroded pyrite to such an es tent that pyrite was almost entirely removed and a bod of massive chalcopyrite was formed. Some chalcopyrit is present as thin veinlets cutting pyrite and filling frac- tures in pyrite. Chalcopyrite is always present in the zinc-rich or bodies; about 15 percent chalcopyrite is present i sphalerite as blebs and corroded relicts 0.02 to 0.03 mi; in diameter. Although massive chalcopyrite was not common in tt specimens studied, specimens from the Grotefend collei tion on display at the California Division of Mines offie in Redding contain banded chalcopyrite-sphalerite oi I and irregular masses of chalcopyrite with minor relic 1 of pyrite. Mammoth Mine, Shasta County 13 Sphalerite. Sphalerite in the Mammoth ore is a red- ish-black variety that probably has a high iron content, t is predominantly massive, with a few recognizable leavage faces as much as 1 mm in diameter. The sphalerite is very unevenly distributed. Tn the ore lined for copper it was present in about equal quantities nth chalcopyrite as irregular lenses and veins, and with halcopyrite in the thin network veinlets around pyrite [rains. I Some ore bodies — for example, the Yolo zinc lens, the il3 ore body, and the 472-raise ore body — are reported by ft. T. Walker 9 to have contained mainly massive sphaler- ;e with irregular lenses and streaks of chalcopyrite and jort of the State Mineralogist, Chap. 7, pp. 313-321, 2 illus., 1923. Price 30*. Maps Map of Shasta County showing mines and mineral resources. Scale 1" = 3 mi., 1939. Price 25*. Outline geologic map of California showing locations of copper properties, by Olaf P. Jenkins. Scale 1 : 1,000,000. Economic mineral map No. 6 — Copper. Price $1.00. Outline geologic map of California showing locations of manganes< properties, by Olaf P. Jenkins. Scale 1 :1,000,000. Economic miners map No. 5 — Manganese. Price 60*. Statewide Reports Copper in California. Bulletin 144, 429 pp., 1948. Price $6.00. Iron resources of California. Bulletin 129, 304 pp., 25 pis., 68 figB, 1948. Price $2.50. Mineral commodities of California — geologic occurrence, economii development and utilization of the state's mineral resources. Bulletii 156, 443 pp., 17 pis., 34 figs., 1950. Price $2.00. Manganese in California, prepared under the direction of Olaf Jenkins. Bulletin 125, 387 pp., 1 map, 46 figs., 1943. Price $3.00. Manganese and chromium in California, by Walter W. Bradle; and others. Bulletin 76, 248 pp., 56 illus., 1918. Price 75*. Geologic description of the manganese deposits of California- supplement to Bulletin 125, by Parker D. Trask and others. Bulletii. 152, 378 pp., 20 pis., 12 figs., 1950. Price $2.75. Economic mineral resources and production of California survey with reference to postwar employment, by Samuel H. Dolbeai Bulletin 130, 219 pp., 3 maps, 1945. Price $1.00. Contains section manganese, pp. 176-179. The lakes of California, by William Morris Davis. Californi Journal of Mines and Geology, vol. 44, no. 2, pp. 201-242, 16 pis 1948. Price 75*. Shasta County lakes, p. 229. Placer mining for gold in California by Charles Volney Averil Bulletin 135, 2nd ed., 377 pp., 4 pis., 106 figs., 1950. Price $2.50. Minerals of California by Joseph Murdoch and Robert W. Webl Bulletin 136, 402 pp., 4 pis., 1 fig., 1948. Price $3.00. printed in California state printinc office 67717 9-52 2M COMPOSITE PLAN OF UNDERGROUND WORKINGS, MAMMOTH MINE, SHASTA COUNTY, CALIFORNIA GEOLOGIC MAP OF THE MAMMOTH MINE, SHASTA COUNTY, CALIFORNIA GEOLOGIC SECTIONS OF THE MAMMOTH MINE, SHASTA . COUNTY, CALIFORNIA SPECIAL REPORT • PLAN OF THE 200 FOOT LEVEL OF THE MAMMOTH MINE, SHASTA COUNTY, CALIFORNIA PLAN OF THE 300 FOOT LEVEL OF THE MAMMOTH MINE, SHASTA COUNTY, CALIFORNIA SPECIAL REPORT 28 PLAN OF THE 470 FOOT LEVEL OF THE MAMMOTH MINE .SHASTA COUNTY, CALIFORNIA 3 + | 1000 IM o o o o o + 1000 N EXPLANATION Porphyritic rhyolite with quorti phenocrysts over 4mm; Dbrt, tuff with quartz phenocrysts over 4mm z < JO- 1 1 I Is APPROXIMATE MEAN DECLINATION 1944 *-- -°-r "'" — -— — y (Geology not knownl^ — ' iPjjLi--- i^^"" «*= B/ a/ D brt Obrb / Dbr Nonporphyritic ond porphyritic rhyotite with quorti phenocrysts lets than 4mm, Dbrb, volcanic breccia; Dbrt , tuft with quarti phenocrysts less than 4mm Pyrite (Closely spaced dots where rock contoins over 90% pyrite) edjpf"-- Outline of ore and ore seom, . — '■* 2784 ore body E^—^ €%' :: Projection of ore above level -—00 •* ABfo^'jStarro / 00 Contact, showing dip (Dashed where approximately located) U D *so Foult, showing dip (Dashed where approximately located; U, upthrowrt side-, D, downthrown side) Strike and dip of beds »rc ^ J&C, Dbr / Ul "5 ^*£ F/ y^JiLeittai ^^<, Clark ore body B G_- Foot of raise or winze Head of raise or winze Underground workings ot altitude of plan 1000 s 1000 s 500 FOOT LEVEL A' b/ (GeologyVot *nown) o ,£'-- ~* ^ ~~~ . Otirt-r Jf&Y V> S N Ifx (Geology not known)