DESCRIPTION OF THE TINTIC SPECIAL DISTRICT.

GEOGRAPHY. there is a steady decrease in the flow of these into four formations : the Tintic quartzite, the Measures. The fossils definitely recognized were wells, showing the dependence of the supply Mammoth limestone, the Godiva limestone, and two species of Syringopora, Productus punctatus, Situation and extent. The Tintic special dis­ upon the melting snow and the spring rains. The the Humbug formation. A complete section (see and zaphrentoid corals. trict is bounded by the parallels of north latitude larger part of the water for the district is piped Section BB on the Structure Section sheet) is Humbug formation. This formation overlies 39° 45' and 40° and the meridians 111° 55' and from Cherry Creek, a stream in the mountains exposed in the region between the towns of the Godiva conformably and corresponds paleon- 112° 10'. It is somewhat over 17 miles in length west of Tintic Valley, 18 miles distant. Eureka and Mammoth. The lowest formation, tologically with it. It is separated, however, north and south by about 13 miles east and west, Vegetation.- The Tintic Mountains bear the the Tintic quartzite, forms Quartzite, Ridge at upon lithologic grounds. It takes its name from having an area of 229.22 square miles. It includes scanty vegetation of an arid region. On exposed the western base of the range, and is followed the mine where it is best exposed. The forma­ portions of Juab and Utah counties, Utah. rocky points grow different species of the cactus. by the Mammoth limestone, which extends east­ tion... consists of a number of beds of Alternating' Topography. The Tintic district includes the The more common trees of the higher slopes are ward beyond Eureka Peak. Above this conies fossiliferous limestones, alternating andsandstones lime* central portion of the Tintic Mountains, with the piny on (Pinus monopJiylla) and the moun­ the Godiva limestone of Godiva Mountain, while with arenaceous limestones and calca­ stones. ; parts of the adjacent valleys. These mountains tain mahogany (Cercocarpus ledifolius). Lower, on the eastern slope of this mountain occurs the reous sandstones, with a total thickness of 250 form in this latitude the easternmost maple thickets occur in the dry ravines, especially Humbug formation. The same series is less com­ feet. Different sections of this formation, how­ Basin ranges. of the narrow mountain ranges which on the eastern slope, while aspens are found in pletely exposed at various points in the southern ever, show a marked difference in the order and rise abruptly from the level valleys of the Great sheltered spots, more commonly those of the portion of the district. ' thickness of these intercalated beds, few beds Basin, and they have the north-south trend char­ northern exposure. All the trees show by their continuing for any distance along the strike. CAMBRIAN c'EEIOD. acteristic of this type of mountains. In total stunted, gnarled, and twisted trunks the severity The formation is doubtless only partially repre­ length this range does not exceed 40'miles, but it of their struggle for existence. In the valleys the Tintic quartzite. This formation consists of sented within this district. . may be considered as continuing to the north in sagebrush (Artemisid) and the rabbit brush clay slates and quartzites. Within the limits Resume. The Paleozoic section in the Tintic the Oquirrh Mountains, and to the south in the (JBigelovia) constitute almost the sole vegetation. of the Tintic district no determinable fossils Mountains includes 7000 feet of Cambrian quartz­ Canyon Range, from which it is separated only by Scattered tufts of grasses occur, but these are were found, either in the quartzite or in the ite capped with clay slates and 6650 feet of lime­ narrow passes. These three ranges have a com­ apparently dead during the summer months. slates. The correlation with the Cam­ stones with a few sandy beds, of which the upper Correlation. mon trend, and are from 5 to 10 miles wide. Culture. The population of the Tintic special brian of the Oquirrh Range, where a 5150 feet are determined from the fossil remains In the northern portion of the district the district is confined almost wholly to the western similar great thickness of quartzite with clay to belong to the Carboniferous. This sequence Tintic Mountains form a well-defined, narrow, and slope of the mountains. The majority of the slates at the top has been found to contain Cam­ in the Paleozoic strata is similar to that which simple mountain ridge, bordered by mines are situated in the area around Eureka brian fossils, is supported by the general geologic has been studied in the Oquirrh Mountains, which wide valleys to the east and west. In Peak, Godiva Mountain, and Mammoth Peak. relations as well as by lithologic similarity. form the continuation of this range to the north. the southern portion of the district important Eureka, Mammoth, Robinson, and Silver City are The exposed thickness of this formation is In the Oquirrh Mountains, however, the upper transverse spurs extend eastward beyond its the towns within the limits of this min­ about 7000 feet, but the base is not found. The portion of the series is much more fully repre­ Towns. boundaries and almost connect this range with ing district, which is one of the oldest quartzite is white in color, weathering sented, indicating an erosion of many thousand the Wasatch. At the northern end of the range in the State. All these iowns are situated on to brownish red on exposed surfaces. itehanedqcuiaytz" feet of strata in the Tintic Mountains. similar low spurs extend to the west. Within the western slope. Homansville was important It is a very pure, compact, and fine­ the limits of the district the crest of these in the early days, and here the first mill and the grained quartzite with occasional beds of fine STRUCTURE. mountains attains an altitude of over 8000 feet, first smelter were erected, while old Tiutic, situ­ quartz pebbles. The lowest beds contain some The main structure of the sedimentary portion Tintic Mountain being 8214 feet. In the north­ ated in the middle of Tintic Valley, was also feldspar and muscovite, while zircon and ru tile of the Tintic Mountains is synclinal. The section ern portion the more important peaks are Packard important as the site of a smelter erected in 1884. grains occur sparingly among the well-rounded described above is that of the western limb of the and Eureka peaks, Godiva Mountain, Mammoth The population of the mining district is estimated quartz grains. Several beds of green, yellow, major syncline, which pitches to the north. The and Sioux peaks, and Treasure Hill. Tintic Val­ at 6500. Two railroad lines connect the Tintic and red clay slates occur near the top of the axis has a general north-south trend and is situ­ ley, bordering the range on the west, has an ele­ mining district with Salt Lake City, which is quartzite. One or two beds of these slates are ated on the eastern slope of Godiva Mountain vation of 5600 feet, and Goshen Valley, on the about 75 miles distant. The Oregon Short Line, found below the highest bed of quartzite, while and Sioux Peak. This western limb is character­ east, is 4500 feet above sea level. The relief is crossing the low divide between Rush and Tintic there are others in the limestone near its base. ized by steep dips, with beds often vertical or marked, and the abruptness of the change from valleys, approaches Eureka and the other towns These strata appear to be conformable, but the even overturned for a considerable distance. On the steep mountain slopes to the almost level val­ from the northwest, while the Rio Grande West­ beds vary greatly in thickness at different points the opposite side of the synclinal axis the dips ley floors is a striking feature. The Tintic Moun­ ern crosses ,Goshen Valley and follows up the within the area. In mapping, the base of the are much less, rarely exceeding 35°. tains, in fact, represent only the upper parts of a valley of Pinyon Creek to the pass just east of lowest bed of limestone has been taken as the A similar unsymmetrical syncline with two mountain mass, the lower slopes and foothills of Eureka. contact, so that some of the slates are included great anticlines make up the Oquirrh Mountain which are concealed beneath the valley deposits. Outside of the mining district this area supports within the Mammoth limestone. to the north, while in the section of Especially characteristic of this portion of the few inhabitants. At the head of Goshen Valley the Canyon Mountains exposed along CARBONIFEROUS PERIOD. range are the canyons or "gulches" which extend a few small ranches are carried on Sevier River the Paleozoic strata are seen to be Agriculture. westward into Tintic Valley. > These Lateral, , , val=, under irrigation, but the more import­ Mammoth limestone. The determination of the folded into an anticline and a syncline. Geolog­ have been cut well back toward the leys- ant part of this valley, including the town of age of Mammoth limestone rests upon the identi­ ically, as well as topographically, the relation of crest of the Tintic Mountains. The most import­ Goshen, is just east of the boundary of the special fication of a single fossil Productus these three ranges is close \ they constitute one ant are Eureka Gulch, Mammoth Basin, Dragon district. In the past these mountains afforded costatus occurring about 1500 feet snur^nand general line of uplift, and exhibit structures Canyon, Ruby Hollow, and Diamond Gulch. The range for cattle, horses, and sheep, but now the above the base of the formation. Upon involving a considerable amount of horizontal principal passes are at the head of Eureka Gulch herbage is so scanty that the grazing is limited to this determination the formation is assumed to be compression of the Paleozoic strata. and of Ruby Hollow. The former has been taken a few herds of horses. probably lower Carboniferous. Thus the Silu­ The structure of the Tintic Mountains, then, is by the line of the Rio Grande Western, and is rian and Devonian may be unrepresented. A synclinal. Minor folds occur in different parts of also an important wagon route from the ranches GEOLOGY. similar hiatus in the geologic succession has been the major folds, and some of these minor plica­ of Goshen Valley to the mining towns of this dis­ found in the Oquirrh Range to the north. In tions are readily distinguished, even when viewed trict. Silver Pass, at the head of Ruby Hollow, The Tintic Range is a composite mountain neither case has it been determined whether the from a distance. In the southeastern part of the is used only for the latter purpose. range, being built up of diverse kinds of rock. possible absence of Devonian and Silurian strata Tintic district an anticlinal axis to the east of

Drainage and water supply. The area of the Like the Basin Rangeso to the. west,' and General_ fea= is the consequence of non-deposition or of uncon­ the major synclinal axis is indicated in the quartz­ Tintic district is tributary to three drainage Wasatch to the east, this mountain tures- formity by erosion. ite and limestone exposed there. Beyond the basins: Tintic Valley, which is tribu­ mass consists primarily of Paleozoic strata. The The Mammoth limestone is named for one of edge of the district another anticline is exposed Streams. tary in turn to Sevier Basin; Goshen nucleus of sedimentary rocks has been in part the oldest and most productive mines of the dis­ in the canyon of Currant Creek; and thence almost Valley, which drains northward by the Jordan buried by volcanic outflows and contains intru­ trict, the workings of which are in this to the base of Mount Nebo, of the Wasatch Range, River into Salt Lake; and Cedar Valley, an inde­ sions of igneous rocks, and all are in part limestone. The formation includes eastward dips are seen in the limestone. On the pendent inclosed basin. Only one perennial concealed by surface accumulations of detrital beds of dolomitic, cherty, and shaly western side of Tintic Valley the Tintic quartzite stream -Currant Creek exists within this area, material. Thus, the rocks occurring within the limestone, which aggregate 4000 feet in thick­ is found dipping to the west, thus showing the and it is not indigenous to the Tintic Mountains, Tintic district are naturally grouped under three ness. At the base the dolomitic limestone is valley to coincide in position with an anticlinal but represents drainage from the slopes of Mount general classes the surficial deposits, the sedi­ dense, and blue, black, or gray in color. Above, axis. In this way the folded Paleozoic rocks are Nebo, in the Wasatch Range. Currant Creek mentary series, and the rocks of igneous origin. occasional beds of pure blue limestone and inter- traced beyond the topographic limits of the Tintic cuts through the transverse spurs of the Tintic Both the sedimentary and the igneous rocks are bedded chert lenses occur, while at the top there Mountains, both longitudinally into the Oquirrh Mountains in a bold canyon at the head of Goshen of economic importance as the country rocks of is a great thickness of shaly, dolomitic limestone and Canyon ranges and transversely to the Valley and flows northward into Utah Lake, fur­ valuable ore deposits. In the legend on the geo­ which weathers reddish. Wasatch on the east and to the West Tintic or nishing water for the irrigation of Goshen Valley. logic maps, these are arranged in the above order, Godiva limestone. This formation, which over­ Guyot Mountains on the west. The channels of the occasional or seasonal streams with the youngest above. Here, the sedimentary lies the Mammoth, is about 2200 feet thick. It Faulting in this region is of minor importance sculpture the slopes of these mountains with deep series will be discussed first, beginning with the takes its name from the mountain on A. pure hme= as compared with the folding. A number of small arroyos. oldest formation, followed by the next younger in the slopes of which it is best exposed. stone- faults can be observed at different Faults. Springs occur at a few points, being more turn. The igneous rocks will be described next, As distinguished from the Mammoth, which is localities, with displacements rarely important on the eastern slope of the range. In and finally the surficial deposits. dolomitic, it is essentially a pure limestone, gray exceeding a few feet. Other faults shown on the general any overflow from these springs or blue in color. In its lower portion a few geologic maps have displacements of from 50 to Springs. is soon absorbed by the alluvium of SEDIMENTARY ROCKS. sandy beds occur; in the upper, the beds are 400 feet. An important fault cuts the limestone the dry channels. At the head of Homansville The series of sedimentary rocks exposed within often carbonaceous, containing many fossils, series between the head of Mammoth Gulch and

Canyon extensive sinking and drifting in the the Tintic district consists mainly of quartzites chieflyJ corals and crinoids,' with occa- Age. of._ Godiva .. the Northern Spy mine, with a displacement of alluvium and bed rock has developed a flow of and limestones of Paleozoic age, having a total sional beds rich in chert nodules and limestone- about 1000 feet. The strike of this fault is nearly water sufficient to supply several of the mines thickness of nearly 14,000 feet. The series has lenses. The fossils taken from these beds show east-west, and it is also characteristic of the other and mills. Throughout the summer and fall been divided, mainly on lithologic grounds, that the Godiva limestone belongs to the Coal faults that they are transverse to the axis of the range. In this feature, as well as in the amount is less rich in these feldspar phenocrysts. Tridymite, horn­ one-half of the area comprised within the limits This belt is about 4 miles long from north to of compression indicated by the folds, the Tintic blende, apatite, and zircon are occasional constituents, while of this district, or more than 100 square miles, south and 2 miles or less in width. It lies wholly magnetite is an almost universal accessory constituent. The Mountains differ from what Las been called the microscopic constituents of this rhyolite show the range from is covered by this andesite and its on the western slope of the range and is deeply typical Basin Range, or faulted monocline. holocrystalline groundmass to the typical glassy base with associated tuffs and breccias. The crest tarnceottSuT* cut by the alluvium-filled Ruby Hollow and Dia­ obsidian . characters. Chemically this rhyolite approaches a TIT! i» i-i PI andesite. « In the Tintic quartzite a considerable amount trachyte. The abundance of free silica crystallizing as quartz, and both slopes 01 this portion ot the mond Gulch. Its western boundary is hidden by of sheeting is to be observed, which commonly however, justifies the determination of the rock as rhyolite. range are of andesite, except a few small areas of the alluvium of Tintic Valley, except at the forms a small angle with the strike and dip, where quartzite, limestone, or rhyolite. Tintic Moun­ northern and southern ends, where its western the latter can be determined. These shear planes The contact between the rhyolite and the lime­ tain, 8214 feet high, the highest peak of the range, limit is indicated by the areas of Swansea rhyo­ are the result of dynamic action incident upon stone on the eastern slope of the Tintic Mountains is composed of flows of this andesite. It is thus lite. the folding of the strata, and are seen also in the is very irregular, the areas of the two preeminently the igneous rock that is most char­ This rock in general appearance closely resem­ overlying slates and limestones. In many places rocks interlocking in a complex man- acteristic of the Tintic Mountains. bles some diorites. Its color, which is light to . . -I-, limestone. the cleavage of the clay slates is very well marked ner. This contact is olten concealed This andesite exhibits considerable variation in dark gray, and its evenly granular and its angle with the beds can be easily deter­ by accumulations of surface detritus, but south of its general appearance. In one locality it may be texture, with the evident importance mined. Along the fractures which are developed Packard Peak, on the northern end of Grodiva a loose-textured, gray rock; in another of its darker constituents, are points of in the limestone there may have been Mountain, the Tetro tunnel cuts the contact, it I«»-IT is ot a dark-purple -11 color, compact_L andComposition texture of such resemblance. Its chemical and mineralogic r f ' f theandesite. more or less displacement, as well as affording an opportunity for careful examination. and glassy; and again it may be bright composition, however, show it to be intermediate adjustment along the bedding planes, but faulting Here there is a considerable thickness of angular green or deep red in color, with prominent pheno­ between a syenite and a diorite i. e., it is a mon­ of this- nature is extremely difficult to detect. blocks of limestone, constituting a heavy talus crysts. Commonly it is not, bright colored, but zonite. This rock varies greatly in appearance. deposit. This has been covered and somewhat dark gray, with a somewhat purple tinge. Usu­ In the northern portion of the area it is perfectly IGNEOUS ROCKS. cemented by the rhyolite. Similar contact brec­ ally rather compact, it often exhibits many of granular, with the lighter and darker constituents Igneous rocks of several distinct types occur cias can be observed in other mine workings, as the vesicular and scoriaceous phases characteristic very evenly intermingled, and this granular phase within the limits of the area here described. well as at a few points on the surface. These of lavas. Almost without exception the Tintic of the monzonite can also be observed at different They are both intrusive and effusive, and include make it evident that when the rhyolitic lavas were andesite is a porphyritic rock showing crystals of localities throughout the area. On the southern rhyolites, andesites, monzonites, and basalt. Taken erupted the old talus-covered slopes of the lime­ both feldspar and the darker constituents. and the eastern edges of the monzonite mass, together, these igneous rocks cover by stone mountain were essentially the same as they however, the rock is decidedly porphyritic. In The Tintic andesite shows considerable mineralogic diver­ far the larger part of the area included are to-day. sity, especially in its ferromagnesian constituents. Biotite, this monzonite-porphyry the crystals of feldspar within the Tintic district. In addition In the central portion of the area of Packard hornblende, augite, and hypersthene are present, together or become more important. Both the granular and separately; thus, several mineralogic types might be separated to their areal importance, some of the igneous rhyolite there is an absence of interbedded struc­ within this area. - The most important porphyry constituent the porphyritic monzonite are compact and hard, rocks are of economic interest, since they are the ture in the rock. Separate flows can packard Peak is the plagioclase, which is chiefly labradorite; biotite and being everywhere jointed, so that the sharp-edged country rocks of important ore. bodies. not, therefore, be distinguished, and |^tperr°0)fable hornblende are less important than the pyroxenes, while of joint blocks are very noticeable in the talus slides. the latter the monoclinic is the more important. In a few The Tintic Mountains have been the scene of this, with the great thickness of rhyo- erupt on* cases, however, the hypersthene is sufficiently predominant to volcanic activity, and the products of that activity lite in this vicinity, suggests that Packard Peak constitute the rock a hypersthene-andesite. Magnetite and The more important constituents of the monzonite are apatite are common accessories, while quartz and olivine are plagioclase, orthoclase, biotite, hornblende, and quartz. Accessory constituents are magnetite, apatite, _ tj. . have been important factors in the construction was the center of an eruption which was of the sporadic in their occurrence. The textures are those typical titanite, and zircon, with secondary chlorite, ofthemon- of the range. The rocks differ considerably in nature of an out welling of viscous lava rather than for andesitic lavas. calcite, epidote, and pyrite. The orthoclase and zonite- chemical and mineralogic composition as well as of an explosive ejection of volcanic material. Such The chemical analysis of a specimen from Tintic Mountain shows this andesite to be characterized by a higher percentage plagioclase are in approximately equal amounts. The latter in appearance, yet they show a general relation­ a location of the eruptive center explains the man­ of the alkalies, and a lower of lime, than is usual Latite rather has a composition varying from that of basic andesine to that of basic labradorite; quartz is usually an important constitu­ ship, and are all directly or indirectly connected ner in which the deep canyon underlying the in typical andesites. The two alkalies are nearly than typical equal in their molecular proportions. Although ent. Of the ferromagnesian constituents biotite is the most abundant and augite the least. The green hornblende rarely with this volcanic activity. present broad gulch in which the town of Eureka this rock, as regards its silica percentage, resembles the ande­ The age of the volcanism in the Tintic Moun­ is situated was filled by the viscous rhyolite. But sites, it is not seen to have a relationship to the syenite- equals the biotite in importance. The chemical analysis of a specimen of this monzonite showed it to be slightly richer in trachyte family. Such an effusive rock, which stands in tains has not been exactly determined. On the few small eruptive masses of rhyolitic rock occur silica than in the alkalies, and poorer in lime than the most chemical composition about midway between the typical basis of general relations it seems A eofvol= in the vicinity of Packard Peak. trachyte and the typical andesite, has been given»the name typical inonzonite, so that it belongs rather to the syenite "latite." The chemical analysis shows the Tintic Mountain phase of this intermediate rock type A calculation of the plausible to assign a Tertiary age to canism- Fernow rhyolite. The Fernow rhyolite occurs mineralogic composition of the rock from the chemical analy­ rock to be essentially similar 'to Ransome's type "latite," sis indicates that the orthoclase probably contains soda, and the igneous rocks. South of the Tintic Moun­ in several small areas in the southern part of the which occurs on the western slope of the Sierra Nevada. tains, where the wash of the southern part of the Tintic district. These appear to represent the that this soda orthoclase would constitute over 32 per cent of the rock, with about 30 per cent of a basic andesine, 16 per range enters the valley of Sevier River, a red northern extension of a mass of rhyolite which On the geologic map the tuff and breccia are cent of quartz, and 12 per cent of hornblende rather poor in conglomerate is exposed, which is correlated with is rather important in the southern part of the not separated from the andesite. Throughout the alumina, with biotite and magnetite constituting the remain­ der of the rock. Quantitatively, therefore, as well as qualita­ the Eocene conglomerate (Wasatch) to the north­ Tintic Mountains. Here, as at the north, the con­ andesite area, however, beds of these Tuffand tively, it is an orthoclase-plagioclase rock. east. Examination of the pebbles of this con­ tact with the limestone is often difficult to trace, pyroclastics are found capping or under- breccia- glomerate failed to detect the presence of any but the relations appear to be similar. The lying the flows of massive andesite, and their asso­ On the southern side of Sunrise Peak the mon­ rhyolitic or andesitic material, although the Fernow rhyolite is like the Packard rhyolite in ciation is so intimate that very detailed mapping zonite is in contact with the andesitic tuffs, and quartzite and limestone pebbles from the Tintic all essential characters, except that it is rather would be necessary to represent the two types sends out well-defined dikes into these Relation of Range are numerous. In the alluvial material, more glassy. A correlation of the two rhyolites separately. These fragmental volcanic rocks are bedded tuffs. One of these dikes can contributed to this same locality from the Tintic is here avoided, since it is probable that they were especially prominent on Volcano Ridge, southwest be traced southeast to a point where it andesite- Mountains, the detritus from the volcanic rocks erupted from two distinct vents, although doubt­ of Diamond and Long Ridge, in the southeastern evidently connects with an andesitic lava flow is rather abundant. On this account the rhyolite less about the same time and under similar con­ part of the quadrangle. Here the tuffs and brec­ overlying the bedded tuffs. On the spur connect­ and andesite are believed to have been erupted ditions. cias are hundreds if not thousands of feet in ing Sunrise Peak with the main part of the range after the deposition of this conglomerate, thought Swansea rliyolite. This rock type is limited to thickness. the monzonite-porphyry of the peak shows a per­ to be of Eocene age. In this way a probable a few occurrences. The principal area is a belt fect gradation into the andesite to the east. Any These pyroclastic rocks vary from the finest stratified tuffs Neocene age is indicated for the igneous rocks of one-fourth mile in width extending from Robinson to very coarse agglomeratic breccias. In the latter, huge separation of the two rock types at this point the Tintic Mountains. Of these rocks, the rhyo­ to Silver City. Separated from this only by the blocks of lava, weighing tons, are mixed with smaller frag­ must be wholly arbitrary. At a lower level, how­ ments of the same material, and are cemented with sand ever, the distinction between the monzonite and lites are relatively the oldest, and the basalt the alluvium of the Robinson basin is a mass of rhy­ matrix of essentially the same composition. The fine-grained youngest, the andesite and monzonite belonging olite which forms the greater part of the hill just tuffs vary in color from brown or green to yellowish white. the tuffs is again sharp. These relations point to approximately to the same epoch of eruption. on the southeastern edge of the village of Robin­ In general they are somewhat lighter in color than the accom­ the monzonite being the intrusive equivalent of the panying lava flows. These tuffs are composed of glass and Three types of rhyolites are distinguished -«- son. These two areas doubtless belong to the fragments of the crystals most abundant in the andesite lava. later flows of Tintic andesite. It intrudes the the Packard, the Fernow, and the Swansea. same rock mass. Although areally' more limited tuffs of the Volcano Ridge series, and these are Packard rhyolite. Areally this rhyolite is an than the other rhyolites, the Swansea rhyolite has The occurrence of agglomerate on Volcano likewise capped by the horizontal lava flows, important rock within the limits of the mining an economic interest as the country rock of the Ridge is of striking interest as indicating the which, it is believed, are the effusive equivalent of district. It extends to the north and east of the well-defined ore vein of the Swansea and South vent througho which much of the ande- An... old vol-, the monzonite. Petrographic and chemical study town of Eureka, and there forms the crest of the Swansea mines. Another occurrence of Swansea site and accompanying tuffs was canfti of the monzonite and andesite fully corroborates range. Its vertical range is over 2700 feet, from rhyolite is that of Horseshoe Hill, near the mouth erupted. Near the western end of Volcano Ridge this field evidence. the summit of Packard Peak eastward to the of Diamond Gulch. this agglomerate contains blocks of limestone Basalt. Although basalt is of common occur­ edge of Goshen Valley. In mineralogic and chemical composition the brought up from below, while immediately west rence south of the Tintic Mountains as well as in the limestone blocks give place to large blocks of The Packard rhyolite shows many variations in Swansea rhyolite is essentially similar to the other parts\ of the Great... Basin, it is Sheets , and white, vitreous quartzite. Some of these are 20 found in only one locality within the dikes> appearance, both in color and in texture. In color Packard rhyolite.J . It differs,' however,' Distinction...... , it ranges from light gray to a bright Composition in the texture of the groundmass, which ^omothef and 30 feet in diameter and are plainly embedded Tintic district. House Butte is a prominent flat- pink and light purple, although often oTpSd6 makes the type commonly termed a rhyohtes> in the volcanic material. With this agglomerate topped hill about a mile west of Tintic Moun­ on the surface the rock is yellowish or rhyollte' "quartz-porphyry." Its geologic occurrence also are associated irregular sheets and dikes of ande­ tain. Here occur three small areas of basalt, the rusty. The texture of the rhyolite shows three distinguishes it from the other rhyolites of the site, the whole presenting rather confused rela­ relations of which suggest intruded sheets. Imme­ distinct varieties. One type is granite-like, its Tintic Mountains, since its relations are those of tions. Surrounding this point is an extensive diately southeast basalt is found in the side of the granular appearance being due to the crowded an intrusive rock. These facts, as well as its area of bedded tuffs which are seen to constitute ravine. In all of these occurrences talus accumu­ phenocrysts. Another type is plainly porphyritic, economic importance, sustain local usage in dis­ the remnant of a deeply eroded volcanic cone. lations somewhat conceal the geologic relations, with the crystals of quartz and feldspars less tinguishing it from the effusive rhyolite of the These tuffs have dips of 10° to 20° and in their but it is reasonably certain that the basalt is abundant than the groundmass. A third type Packard Peak area and of the area to the south. strikes express a roughly semicircular arrange­ intrusive in the andesite. This rock is black and shows glassy textures, all being banded, often The Swansea rhyolite is light gray in color, with pheno­ ment. The agglomerate locality is approximately very compact, lacking the vitreous texture of the porous and vesicular. In this type crystals are crysts of flesh-colored feldspar and clear .quartz more or less at the center of this area of tuffs. The occurrence darker of the andesites. It is very fine-grained, abundant, but with a few traces of the presence of a darker of included fragments of rhyolitic lava in this and no megascopic crystals can be seen. Its micro­ rarely seen, and in some occurrences it id an constituent. The rock is commonly considerably altered, the almost black obsidian. feldspars being usually clouded and often completely altered. andesite agglomerate indicates the relative age of scopic constituents are olivine and augite in a Ari interesting constituent in one occurrence is tourmaline. the two lavas. holocrystalline groundmass of feldspar and augite. The megascopic phenocrysts are quartz, feldspar, and bio- This occurs in aggregates of acicular crystals, which in part tite, the latter being often the most prominent. Quartz Monzonite. The area lying south of Robinson replace the feldspar and in part occur in the groundmass of RELATIONSHIPS OF THE IGNEOUS ROCKS. appears almost universally, its angular crystals often project­ the rock. and Mammoth, and extending past Treasure Hill ing from the weathered surface. In some occurrences of this rhyolite the fresh crystals of sanidine are large and so abun­ Andesite. This rock occurs principally in the and Diamond to Sunrise Peak, is characterized by Four types of igneous rocks have been described dant as to make the rock much lighter colored than when it southern part of the Tintic district. Nearly a rock locally termed " granite " or " porphyry." above as occurring in the Tintic district: rhyolite, 3

andesite, monzonite, and basalt. No analysis was alteration may act under superficial conditions purely surface erosion. Quartzite is affected both angle in the shore, thus forming a natural reser­ made of the basalt, which is of little importance within the range of our observation, or the pro­ by temperature changes and by frost, but suffers voir. Sections of the wave-built terraces and in the Tintic district. The following table shows cesses may be such as to operate only at great little solution. bars show well-bedded sand, fine and well sorted. depths under conditions known to us only through A few thin beds of coarse gravel occur inter- the analyses of the Swansea rhyolite, the Packard STIRFICIAL ROCKS. rhyolite, the Tintic andesite or latite, and the inference. The separation of the two classes is bedded with the sand. This gravel can be traced Sunbeam monzonite. not always easy, since the same rock may have A thick mantle of disintegrated rock material upward to the talus at the base of steep slopes of been subjected to both kinds of alteration. The covers a large part of the Tintic special district. limestone. The deposits thus indicate an alterna­ Analyses of igneous rocks occurring in the Tintic district. [Analyst, H. N. Stokes.] superficial processes and reactions may be included This constitutes one of the most unfavorable con­ tion of conditions now the locally derived lime­ under the term "weathering," while those that ditions for geologic work, and has often seriously stone fragments being deposited on the beach, SWANSEA PACKARD ANDESITE, RHYOLITE. RHYOLITE. OR LATITE. MONZONITE. are deeper seated, or abyssal, may be comprised interfered with exploration for ore bodies. On and now the finer shore drift. Calcareous tufa under the term " metamorphism." the geologic map two of these surficial formations has been deposited on the upper surfaces of the Per cent Per cent. Per cent. Per cent. The rocks of the Tintic Mountains have been have been distinguished, the alluvium and the uppermost pebbles of these beds. SiOs ...... 71.56 69.18 60.17 59.76 subjected to metarnorphic processes, and although Bonneville lake beds. Faint traces of other shore lines can be detected, Tin .38 .69 .87 .87 these are less important here than in many regions, Alluvium. Tintic Valley is bordered by allu­ but what has been called the Provo shore line, Al O 14.28 14.37 15.78 15.79 although strongly marked at other localities, is Pr O the closely related processes of ore deposition are vial cones which extend down from every ravine TTp O of greatest moment. The closely folded Paleozoic and valley along the western edge of not indicated here. There is, however, a conspic­ .89 2.52 3.42 3.77 Alluvial fans. FeO...... 57 2.95 3.30 rocks have been somewhat affected by the Tintic Mountains. These cones of uous topographic feature directly connected with Dynamic MnO...... 10 .11 .12 dynamic metamorphism. The sheeting metamor= stream-deposited material become flatter as they the Provo stage of the lake. Currant Creek phism. BaO ...... 28 .09 .14 .09 and crushing along certain zones have emerge from the mouths of the ravines and emerges from its canyon immediately SrO...... "f*T»a f»o .09 reduced massive limestone to a shale-like rock, gulches, and here better deserve to be termed east of the Tintic district, and from CaO ...... 1.18 1.88 4.69 3.88 the mouth of this canyon extends a large delta MgO ...... 42 .70 2 52 2.16 which in turn is locally decomposed to a plastic alluvial fans. Near the center of the valley the K o 4.37 5.00 4.16 4.40 clay. Since the processes of mountain folding slopes are very gentle, yet the grade is sufficient which forms a noticeable interruption in the ]« n 3.00 3.58 2.96 3.01 antedate the eruption of the igneous rocks, the for the wide transportation of coarse material. broad concave sweep at the head of Goshen Val­ Lis O...... latter have been little affected by dynamic action. The exceptionally large proportion of run-off due ley. The surface of this delta has an elevation H s Oat 110°.-...... 36 .35 .25 .31 A more important type of metamorphism is to the cloud-burst character of the rainfall of this of slightly more than 4700 feet, thus approximat­ H 2 O above 110°.. .79 .25 1.23 1.11 one in which water is the principal agent. This region gives to the occasional streams a greater ing the level of the Provo shore line as seen else­ Po .13 .26 .42 .40 where. Below, the delta face has a deep slope to VasV.O, ...... 02 .01 .01 02 has been termed hydrometamorphism. Hydrometa= capacity to transport than might be expected. morphism. Mo...... trace Changes due to this type of alteration Evidence as to the manner of transportation is the valley bottom, and Currant Creek has now As ...... 4-»»Q f*A are mineralogic. Thus it is a fact that in the seen in the angularity of most of the rock frag­ cut a deep channel in the delta terrace. The 01...... 06 .04 .04 igneous rocks secondary minerals are of common ments found near the middle of the valley. origin of this delta is connected with the desicca­ PO .78 occurrence. Such minerals resulting from hydro­ Their journey from the rock slope to the outer tion of the lake. When the water stood at its FeS8 ...... 2 29 metamorphism are chlorite, epidote, muscovite or edge of the alluvial fan has been a comparatively highest level, or the Bonneville stage, Currant Total...... 100.01 99.55 99.79 99.83 sericite, serpentine, talc, magnetite, and pyrite. rapid one, and they have suffered less corrasion Creek Canyon was a narrow strait connecting the In the northern half of the monzonite area there than would be incident to transportation in a water in Juab Valley with that in Goshen Valley. From these analyses it is seen that the rhyo- are several large masses of bleached rock. In well-defined stream channel. With the fall of the lake water to the Provo level lites have similar compositions, and that the two many cases the true nature of this rock is difficult The structure of these alluvial fans can be there was a marked change of conditions; Cur­ other rocks likewise show chemical affinities. The to determine. In appearance the rock can be seen seen where the deep arroyos are at present rant Creek began to drain Juab Valley, having andesite is plainly the effusive equivalent of the to have the same texture as the other monzonite. trenching them. They show stratifica­ its point of discharge at the head of Goshen Val­ monzonite. The slight differences in chemical The rock is not at all disintegrated or less tion, sometimes imperfect, but usually g"aevrebieandd ley. Here the delta was doubtless quickly built, composition of these two rocks are much less compact than the fresh rock. Analysis shows, readily distinguished. The materials and its upper surface may be taken as indicating important than their similarity, which is especially however, considerable chemical change. The are interbedded gravel and coarse sand. The the water level at that time. The uniform fine­ striking in those features which may be termed monzonite has lost the most of its iron oxide and freshness of all this detrital material is noticeable, ness of the material composing the Currant Creek characteristic of the two rocks. Such are the all its lime, as well as all its soda. There is, since rock disintegration has been so far in excess delta is due probably to the fact that all coarser relative importance of the alkalies as contrasted however, a relative gain in potash and silica, as of rock decomposition. sediments were deposited in the lake-like expanse with the lime and the potash-rich character of the well as of water. Thus the rock has been silici- In many cases the alluvial deposits extend far of the stream in Juab Valley above the canyon. two rocks. In mineralogic composition and tex­ fied as well as leached. up into the mountains, following the different Talus deposits. These deposits, although not ture the relationship of the two is not so apparent ; The processes of superficial alteration have indicated on the geologic maps, are very exten­ drainageo lines,> and their distribution is,> Distribution . ,... ^ both rocks contain labradorite as an essential con­ furnished the material for the extensive surficial therefore, greater than can be repre- ofalluvium- sive in some portions of the district. They stituent, but they differ somewhat in their ferro- deposits which are described below. sented on the geologic map. In sinking the wells include the rock detritus which occurs in the Weathering. magnesian constituent. In the andesite or latite These processes have modified the sur­ near Homansville, alluvium was found in one form of talus slides and avalanche streams. The the pyroxenes are characteristic, with Monzonite face of the region and have also affected the rocks instance to a depth of 65 feet, consisting of inter- material is heterogeneous and unstratified and biotite less important and hornblende and latite- and ores lying nearest the surface. The zone of bedded clay and gravel, the former in beds a few owes its removal from the original rock mass pri­ only accessory. In the monzonite, biotite and such alteration is that above ground-water level. inches thick. The alluvium of the hills and marily to the action of gravity. Creep due to the hornblende are more common than augite. In the Within this zone the action is that of oxidation, ravines above Goshen Valley is similar to that action of frost and snow may occur in these talus latter rock orthoclase and quartz are rather impor­ hydration, and carbonation, all resulting from the on the west side of the range, and does not slides, while on the steepest slopes avalanches of tant constituents, while in the latite quartz is very chemical activity of the surface waters and their require further description. snow doubtless have been effective in the trans­ rare and orthoclase was not detected. This is to occluded gases. Under this head also are to be ^Bonneville lake beds. Goshen Valley is about portation of the rock fragments to lower levels. be explained by the fact that in a monzonite these included the physical changes due to tempera­ 1000 feet lower than Tintic Valley and is covered Well-defined avalanche streams occur in some two minerals are the last to crystallize, and would ture variations, or water and frost action. At the by deposits of a different character. The allu­ ravines, and these have apparently not yet come therefore be wanting in the effusive equivalent surface the action is, for the most part, physical vium, which doubtless once covered the lower to rest, judging from the comparative absence of where the consolidation of the glassy base pre­ rather than chemical. Disintegration of the rock part of the valley as it yet covers the whole of vegetation on their surface. vented their crystallization. mass takes place with comparatively little decom­ Tintic Valley, has been hidden from view by In many places on the slopes of the Tintic The two rh}rolites contain 1 to 12 per cent more position of the mineral constituents. Thus, in lacustrine deposits, which are finer grained and Mountains the mantle of talus material has accu­ silica than the monzonite-latite type, and are much the areas of igneous rocks coarse mineral sands more evenly distributed. The Pleistocene lake mulated to a great thickness. Pros- Cemented poorer in the alkaline earths. The latter type, on are of frequent occurrence, which are the result which covered the eastern part of the Great Basin pect tunnels, both in limestone and talus- the other hand, is slightly richer in alumina, and of the action of frost and sudden temperature extended into this valley, and this fine material monzonite, show disintegrated rock to a depth of contains more of the oxides of iron as well as of changes. Wind erosion is also an important fea­ now covering the surface was deposited from the 50 or even 100 feet. So compact is this detrital the titanic and phosphoric acids. The chemical ture on the exposed" rocky peaks. waters of Lake Bonneville. material that roofs and walls have remained characteristic of this group of rhyolites, monzo­ Of the igneous rocks the monzonite is the most The Bonneville shore line, which marks the standing untimbered for many years in these nite, and latite, is the constant molecular ratio resistant to atmospheric agencies^ being broken highest water level, is well developed at the head deserted tunnels. In gulches also, where streams have cut trenches in the debris, the high angles between the potash and the soda, which is nearly into angular blocks which form a pro­ of Goshen Valley,J ' a few feet above the Old_,. shore. 1: 1, the soda being always slightly in excess. tective mantle. The andesite breaks Relative 5100-foot contour. The terrace here is line< at which the walls stand show a considerable resistance. This relation of the alkalies may be regarded as into smaller angular fragments, and in mostly cut in alluvial material which extends degree of cohesion. This cementation of loose the best evidence of consanguinity in the igneous the more porous lavas there is a marked tendency down from the small ravines indenting the moun­ fragments into such coherent masses is a process rocks of the Tintic Mountains. It is to be noted, to disintegration into sand, which is washed from tain slope. As shown in Mr. Gilbert's monograph* connected with the aridity of the region. Chem­ also, that both the rhyolitic type and the monzo­ the slopes and accumulates in hollows. The on the Pleistocene lake, this area formed a part ical decomposition of the rock fragments has nite-latite type approach trachyte in mineralogic rhyolite weathers like the andesite, but is slightly of Utah Bay, an almost landlocked arm of the been slight, but sufficient water circulates through and chemical composition. less resistant. In their resistance to weathering lake; therefore, the waves which beat on this the deposits to leach out a small part of their sol­ action the sedimentary rocks stand in the follow­ shore having but little fetch and being relatively uble constituents. Such solutions are brought to ALTERATION. ing order: quartzite, limestone, sandstone, shale. inefficient, the shore line is not so deeply carved the surface, so that on evaporation the material The Tintic Mountains are in great part com­ The shale and sandstone yield to both frost action as at more exposed points; yet the terrace mark­ in solution is left near the surface, where it acts posed of comparatively young rocks, and their and solution, the latter removing the cementing ing the Bonneville level is readily observed, since as a cement. history has been relatively simple, yet material and thus disintegrating the rock. The it forms the line of division between two types of GEOLOGIC HISTORY. these rocks show in their general as limestone is broken into fragments by the frost topography. Above, the rock has been sculptured ..,. . . . . morphism. well as their microscopic appearance on exposed points, and also suffers a certain into bold outlines which even the surface accumu­ Several epochs in the history of this region are changes due to processes which have been active amount of solution. This is most apparent where lations of rock detritus do not conceal. Below, recorded by the different rocks and deposits subsequent to the formation of these rocks. Such the Godiva limestone contains chert nodules, the lines are softened and the gentle, even slopes which cover the surface. Although the region changes express the effect of varying conditions which stand out relatively unaffected. The caves of the lacrustine deposits afford a marked con­ has been one of constant change and unceasing and may all be included under the term "altera­ occurring in the limestone at the surface are trast. One interesting feature of the Bonneville geologic activity, four general;epochs in the geo­ tion." These changes have been both mineralogic closely related to fissures, and may have an origin shore line is a bar constructed across a reentrant logic history may be distinguished. and structural, and have been effected by both similar to that of the caves encountered in the Sedimentation (Paleozoic). The history, as chemical and physical agencies. The processes of mines of the region, and thus not be the result of * Lake Bonneville: Mon. U. S. Geol. Survey, Vol. I, 1890. recorded in the rocks, begins with Paleozoic sedi- Tintic Special. 4 mentation. Nothing is exposed below the Tintic deposited. These beds of mixed sediments were commencement of the eruption. Similar erup­ up into the mountains the mantle of alluvium is quartzite, which is believed to be of Cambrian also limited in extent, so that the rocks as now tions occurred in the southern part of the district, considerable. Alluvial deposits of this character age. The position of the Cambrian shore line seen are not persistent in character along the as well as contemporaneous intrusions of rhyolite and extent testify to climatic conditions favorable and the conditions which governed the deposi­ strike. in the central portion of the area. to both erosion and transportation. At present tion of the 14,000 feet of Paleozoic sediments can Uplift and erosion (Mesozoic). This area of Following this volcanic activity were the erup­ the agencies of transportation are inadequate, so only be inferred. Paleozoic sediments is believed to have been tions of andesitic lavas, quite different in character. that the rock detritus accumulates in talus depos­

In the first place it is to be noted that there is raised above sea level early in Mesozoic time. Volcanic cones were built up-L byJ the Andesitic. , ., its. It is evident, therefore, that a period charac­ in the Paleozoic section of the Tintic Mountains Although sediments of Mesozoic age occur both lava flows and the accompanying frag- eruPtlons- terized by greater precipitation preceded the no apparent stratigraphic break, such as a marked to the east and to the south, none are found mental material, which was ejected in great quan­ present one of aridity. The lacustrine deposits unconformity or an extensive conglomerate. within this area, and it probably was situated in tities. A later eruption in the Diamond area of the now extinct Lake Bonneville afford further These would be expected as the result of any the southeastern part of the Mesozoic continent. was less explosive in character, and appears to evidence of this in Goshen Valley, where the lake considerable uplift or subsidence. The absence In the Tintic Mountains the Carboniferous have been of the nature of a quiet extravasation beds were deposited, covering the alluvium of of coarse material in any of the sedi­ strata have suffered compression to a consider­ of lava from a fissure. The outlines of this fissure that valley. Later, when the rainfall' became ments is noteworthy, a few pebbly Coasres"csedi= able extent. At what time such folding took are approximately defined to-day by the area of insufficient to maintain this body of water, it bands in the Cambrian quartzite being place can not be determined within monzonite and andesite-porphyry, rocks which disappeared. Since that time these deposits have the only exception. The sediments are all such the limits of the Tintic district, but palSi? consolidated below the surface. Higher up, remained practically undisturbed. Currant Creek i i T -i -i /-^i rocks. as to show that their deposition at no time immediately to the south, in the (Jan- andesites flowed from this fissure, covering the trenched its delta as the lake level was lowered, occurred near a shore line. As compared with yon Range, it is seen that the Carboniferous fragrnental deposits and lavas of the older vol­ cutting down over 100 feet into the delta depos­ the Paleozoic rocks of the Wasatch Mountains to limestones continue the folds of the Tintic cano. A Tertiary age is given to these volcanic its. The lowering of Lake Bonneville, with the the east, the Tintic sediments above the top of Mountains, while early Tertiary conglomerates rocks on the basis of general relations. sudden change of water level, also caused an the Cambrian quartzite are characterized by their in the same locality show only a slight tilting. Deposition of surficial formations (Neocene increase of efficiency in other streams tributary generally calcareous nature. In the Paleozoic of So marked an unconformity between the Tertiary and Pleistocene). Erosion continued its work to the lake. In Tintic Valley there are stream the Wasatch Mountains arenaceous and argilla­ and Paleozoic rocks makes it evident that the even before the cessation of volcanic activity. terraces which are referable to this period of ceous rocks greatly predominate throughout the mountain-building movements which caused these The rhyolitic flows were somewhat eroded pre­ marked activity, but in the rich bottom lands of section, while in the Tintic series above the Tin- folds were of Mesozoic age. They may have been vious to the first eruption of andesite, while the this valley there is little other evidence of the tic quartzite and associated shales only 110 feet i connected with the birth of the Mesozoic conti­ volcanic cone of Volcano Ridge had begun to stream that once flowed. Along the edge of the of sandy limestone and quartzite occur with 6500 nent. be carved by atmospheric agencies before the valley -alluvial fans are still being trenched by feet of limestones. This points to the existence This uplift inaugurated a decided change in intrusion of monzonite cut across one side, and the occasional streams. of a deepening sea over the Tintic area after the history of the area. Erosion was substituted the flows of andesite covered the earlier volcanic Resume. In Paleozoic time the area was one

Cambrian time with conditions that were favor­ for sedimentation and the new land Extensive deposits. Since then erosion has continued with­ of sedimentation. Beginning with the deposition able for limestone deposition, while to the east area immediately began to waste at its erosion. out interruption, and to-day the region is one of of well washed sand, the succeeding sediments arenaceous sediments were being deposited nearer surface. Many thousand feet of Carboniferous marked relief, although the products of Tertiary were calcareous muds followed by more argilla­ the shore. strata have probably wholly disappeared from the volcanism had concealed to a large extent the ceous and arenaceous sediments. This series, The Mammoth and Godiva limestones record Tintic region, and their erosion was pre-Tertiary. earlier work of erosion. which comprises thousands of feet of sediments, a long interval of sedimentation under conditions Such a thickness of overlying strata was doubt­ An exact measure of this post-volcanic erosion was deposited in the deeper waters of the sea, essentially uniform. They are not rich less necessary for the production of the close can not be easily given. The upper slopes of and, for the most part, at a considerable distance in fossils, and it is also noticeable that semmenta= folds which characterize the structure of the Car­ Godiva Mountain do not appear to from the shore. the fossils found were from a few well- boniferous rocks of the Tintic Mountains. have been greatly reduced, although po t°=vo*c°anic In Mesozoic times these sediments were lifted defined beds in which, although the rock is Volcanic activity (Tertiary). The third epoch the,, volcanic-, materiali 1 covering theA? erosion. above the sea level and the horizontal beds were markedly fossiliferous, the range in species seems in the history of the Tintic Mountains is that lower slopes has been in part removed, yet the compressed into close folds. Atmospheric agen­ to be decidedly limited. Thus it appears that of volcanism. The mountains had been deeply bottom of the pre-volcanic canyon at the head of cies immediately began to wear away these rocks, the conditions were not especially favorable to carved by erosion, portions of the range being Eureka Gulch has not yet been reached. In the giving a marked relief to the Tintic Mountains. organic life. A break in these uniform condi­ reduced nearly to the valley level, when volcan­ southern part of the Tintic Mountains evidently In Tertiary time volcanic eruptions of tuff and tions seems to have been inaugurated with the ism began its task of rejuvenating the mountain a large amount of the volcanic rock has been lava added greatly to the mass of these mountains, deposition of the Humbug formation. Here range. Deep canyons were filled with volcanic removed by erosion. Buckskin Mountain and and the results of the Mesozoic erosion were arenaceous, argillaceous, and calcareous beds material, thus restoring in great measure the topo­ Tintic Mountain have been carved from horizon­ largely concealed. occur in succession, in consequence of more varied graphic continuity of the range. tal flows of andesitic lava. Andesite once cover­ Since the volcanic eruptions, erosion has cut conditions of sedimentation; the depth of water The earliest lavas to be erupted were the rhyo- ing the monzonite of Sunrise Peak and the area deeply into the accumulations of volcanic mate­ was doubtless somewhat lessened, so that arena­ lites. From the vicinity of Packard Peak an to the north has almost wholly disappeared. rial and the products of this erosion have been ceous as well as calcareous material was contribu­ outwelling of viscous rhyolitic lava Rh olitic Some measure of the amount of erosion in the deposited as alluvium and lake beds in the val­ ted to the area of deposition, and, changing cur­ filled the deep canyon north of Godiva eruPtions- Tintic Mountains is afforded by the extensive leys and as talus on the upper slopes. rents being only partially able to perform the Mountain and Eureka Peak, and the lava also surficial deposits.Jt In Tintic and Surficial...... GEORGE OTIS SMITH, task of sorting this heterogeneous material, calca­ flowed off to the southeast, down the Goshen Goshen valleys the alluvial and lacus- dep°sits- Geologist. reous sandstones and sandy limestones were slope, making the range much wider than at the trine deposits are doubtless very deep; even well June, 1899.

MINING INDUSTRY. rich in ore deposits. This includes the Godiva, Homansville in 1871. The second, the Tintic to the large smelters in the vicinity of Salt Uncle Sam, Humbug, Utah, and Sioux mines, Milling and Smelting Company's works at Dia­ Lake City and elsewhere. The shipping mines HISTORY. which are situated on the eastern slope of Godiva mond,' was also built in 1871. The Local. , in 1899 were: the Mammoth,' Bullion- Producing_ . . Tintic is one of the oldest mining camps in the Mountain and Sioux Peak. third smelter was the Copperopolis, sraelters- Beck, Centemrial-Eureka, Grand Cen- mines- State. Ore was discovered by a party of pros­ For a number of years rapid development of built in 1873. Others were the Crismon-Mam- tral, Gemini, Eureka Hil], Swansea, South Swansea, pectors returning from western Utah in Decem­ the mines in this district was not possible, owing moth, built at Tintic in 1884; the Latham furnace, Godiva, Humbug, Uncle Sam, Sioux, Sunbeam, ber, 1869, and the districts were organized in the to poor facilities for transportation. There was, built at Goshen in 1874; and the Clarkson, at Ajax, Star Consolidated, Four Aces, Carissa, Joe following spring. The only districts in the State however, a very considerable amount of ore near Homansville. Like the earlier milling processes, Bowers, May Day, Northern Spy, Eagle, Treasure discovered previous to Tintic were those of Bing- the surface which was rich enough to be mined smelting was unsuccessful. Hill, Lower Mammoth, Tesora, Alaska, Shower's ham in 1863 by the soldiers of Gen. P. E. Connor; in the face of almost any difficulty. These rich The process of leaching the ores has been tried Consolidated, Boss Tweed, Utah, Rabbit's Foot, Rush Valley, or Stockton, also in 1863; and ores were shipped to San Francisco, on two occasions once at Goshen, in 1876, and and Silver Park. The Tintic iron mine shipped Little Cottonwood, in 1868. The first claim California; to Reno, Nevada; to Balti- again on the site of the old Miller mill, nearly 600 cars of iron ore to be used as flux. It recorded in the Tintic district was Early_, , loca=, more, Maryland; and even to Swansea, Wales. in 1879. This method of winning will be noted that the above list of producing called the " Sunbeam," and was located tions- The average value of the ores was not sufficiently values was even less successful than milling and mines includes three of the four mines first loca­ on December 13, 1869. The second location, the great to warrant shipment to such distances, and smelting. ted in the district, a fact which speaks well for Black Dragon, a short distance north of the Sun­ attention was turned at an early date to the The scant supply of water contributed largely the permanence of the ore bodies. beam, was made on January 3, 1870. The third erection of mills and smelters in the vicinity of to the want of success in the early mills. The location was made on February 26 of the same the mines. The first mill erected was at Homans- Mammoth and Farrell mills are to-day supplied PRODUCTION. year, on the site of the present Mammoth mine, ville, in May, 1871. The second mill in the same through a pipe line from Cherry Creek, 18 miles In the first few years after the discovery of and two days later stakes were set on the Eureka locality was completed in the fall of the same to the west; while at Eureka this supply is aug­ precious-metal deposits in these mountains the Hill ledges. year. The Wyoming mill, the Miller mill, the mented by water from wells sunk at Homans­ production was about equally divided between These early locations were in parts of the dis­ Shoebridge mill, southwest of Dia- Amal ama_ ville. the deposits in the sedimentary and those in the trict which have continued to be the important mond, and the Copperopolis mill were tion mills' The development of the mines was greatly igneous rocks, or between the northern and the centers of the mining industry. The Mining constructed in 1873; the Mammoth mill, at Tin- accelerated upon the advent of the railroads the southern districts. Upon the exhaustion of the first is in the area of igneous rock centers- tic, in 1879; the Roseville mill, southeast of Oregon Short Line from the west in 1883, and oxidized ores in the igneous rocks the output of in the southern part of the district, in the Mammoth, at about this time, and more recently the Rio Grande Western from the east in 1891. the southern portion of the district became prac­ vicinity of Silver City. The next area north is the present Mammoth mill, at Robinson, in There are now four pan-amalgamation mills of tically nothing, and most of the mines were aban­ that of Mammoth Basin, the most important December, 1893; the Eureka Hill and Bullion- the most modern type in the district: the Mam­ doned. A few, however, pushed their shafts to mine of which was the third location of the dis­ Beck mills, at Eureka, in 1894; and the Farrell moth and the Sioux or Farrell mills at Present_ con- greater depths, until, finally, after a lapse of trict. North of this basin, and separated from it mill, at Robinson, in 1895. Robinson, and the Eureka Hill and ditions- nearly twenty years, rich sulphide ores were by a high ridge of limestone, is the Eureka area, Owing to the poor success of the early amalga­ Bullion-Beck mills at Eureka. These treat suc­ found in several of the mines, notably in the with the Bullion-Beck, Eureka Hill, Centennial- mation mills and the refractory nature of much of cessfully the lower-grade ores of the district and Swansea and South Swansea. Since then these Eureka, and Gemini mines. East of the Eureka the ore, smelting has been tried frequently. The ship both bullion and concentrates. mines have produced constantly, and the renewed and Mammoth groups of mines is another locality first smelter erected in the district was built at The richer ores from the mines are shipped interest in the veins of the igneous rocks that 5 their developments have created has already fractures are most common along the contact of trend N.-S., but turn gradually to the west, and sequently to the N.-S. fracturing; this fault is accelerated development in other mines and the Robinson quartzite and the Eureka lime­ between the Eureka Hill and Bullion-Beck shafts traced up to but does not enter the rhyolite, the added greatly to the production of the district. stone, where they have a maximum displacement are mainly N. 35° W. North of the Bullion-Beck earliest of the igneous eruptives, hence A eof(rac From the earliest times the mines in the sedi­ of 200 feet. These fractures are almost always shaft they trend within a few degrees of N.-S. must have been formed previous to vol- tures< mentary rocks have been productive, and the vertical. In the two southern mines the ore bodies are canic activity. As the most recent sedimentary development has kept so far ahead of the actual The subordinate fractures, which, while con­ fairly continuous and extend to great depth, but strata belong to the Carboniferous age it is prob­ breaking down of the ore in the stopes that the stantly present, are much less persistent than the in the north they are less continuous; they have able that their deformation, and the subsequent production has been one of constantly increasing other fractures, have the following a small vertical range and consist of a number of mineralization, occurred during Jurassic time, or proportions. directions: NW., 1ST. 35° W.; N. 20° W., lens-shaped bodies scattered widely throughout at least prior to the Tertiary, which was the age The following table, compiled from the reports and NE. They are usually vertical, but those the ore zone. But very few later or secondary of volcanic activity. of the Director of the United States Mint, affords which are parallel to the strike of the rocks are fractures were observed in this zone. FEACTUEES IN IGNEOUS BOOKS. the best data on production obtainable. The also parallel to the dip. The N. 20° W. and N. Mammoth zone. This zone commences on the individual reports of production from the various 35° W. fractures are the most abundant. The north at the Eagle mine, and extends thence The fracturing in the igneous rocks occurs mines have been used, so far as possible, as a latter are confined to sharp flexures in the strati­ southward through the Grand Central, Mammoth, mostly in the more solid types, the monzonite check on this table, but, as it has been impossible fied rocks along Eureka Gulch, and are accompa­ Ajax, and Lower Mammoth mines. The most and quartz-porphyry, and is most abundant in the to get reports on all the mines, and as many of nied by much brecciation of the strata. In the prominent and most numerous fractures have a more coarsely granular of these rocks. the reports are incomplete, the production of the former the individual strata have slipped past general N.-S. direction. N. 25° E. and NE. frac­ The mineral-bearing fractures have a maximum earlier years has not been verified. each other, forming open spaces of small dimen­ tures are common to all the mines of the zone, development between Silver City and the Sun­ sions. and are especially well seen in the Ajax, where beam mine, becoming few and insignificant east Production of the Tintic mining district. The interrelations of the various fractures are they have been extensively mineralized. The N. of the latter. Some mineralized fractures have very complex. The majority of the fractures 15° E. fractures are peculiar to the Mammoth also been developed in the porphyritic monzonite YEAR. Gotn. SILVER. cross, but appear not to have faulted Intersectjons mine, where, together with the N.-S. fractures, on Treasure Hill and Sunrise Mountain. Ounces. Ounces. one another. The exceptions to this offractures- they have been found on planes of heaviest min­ There is not so wide a range in the trend of 1880 ...... 3,012 8,682 that have been noted are along Quartzite Ridge eralization. N. 20° W. and NW. fractures have these fissures as in the sedimentary rocks. Fis­ 1881 ...... 2,332 105,354 and the Spy-Ajax fault, where N.-S. fractures are their greatest development in the Grand Central sures trending N. 15° E. and N. 35° E. Trendof 1882 ...... 3,000 232,558 1883 ...... 2,000 224,800 faulted by E.-W. fractures; also in the mines of mine, and are apparently the result of slipping are the most abundant. N.-S. and N. |j eluuf in 1884 ...... 1,500 612,016 Eureka and Godiva mountains, where N. 25° E., on the planes of stratification. 10° W. fractures also occur, the latter 1885 ...... 868 868,925 N.-E., and E.-W. fractures are seen occasionally The Spy-Ajax fault, which crosses this zone, being limited to mines north of Silver City. A 1886 ...... 2,300 825,000 to break the continuity of the other fractures. has displaced the strata on the south side a few have a trend N. TO0 E. They are always 1887 ...... 3,200 1,412,463 The N.-S. fractures, which are by far the most thousand feet to the eastward. Adjacent to this nearly vertical, the dip rarely being less than 80°; 1888 ...... 7,110 1,201,620 common, are also most abundant on the west limb fault on either side are many parallel fissures, but it is not uncommon for the dip to change 1889 ...... 14,940 2,055,700 1890 ...... 24,633 3,801,700 of the syncline, where the strata are nearly verti­ some of which are ore bearing. The exact rela­ from east to west within a hundred feet. The 1891 ...... 19,444 2,901,730 cal. On the east limb, where the strata dip at tions of the ore bodies on the north to those on fractures all die out near the sedimentary rocks. 1892 ...... 16,470 2,011,642 low angles, they are not common. The NNE. the south of this fault are not clearly understood. In the mines north of Silver City the Swan­ 1893 ...... 15,097 1,990,860 and NE. fractures are most common at the south­ At the southern end of the Mammoth mine, at sea, Park, Four Aces, and Silver Bow N. 10° 1894 ...... 18,066 2,582,033 ern end of the syncline, where they cross the the intersection of several fissures, the ore forms W. and N. 15° E. fractures predominate. On the 1895 ...... 27,525 3,517,166 beds nearly at right angles. The E.-W. fractures a large, elliptical shaped chimney, which has north side of Dragon Gulch, N. 20° to 35° E. -1896 ...... 40,470 3,955,843 1897 ...... 37,039 2,877,600 are found in the central and northern parts of been traced continuously for more than 1600 feet fractures are the more common, and in the mines 1898 ...... 38,136 3,389,507 the area of stratified rocks. The NNE., NE. and in depth. This sends off several fingers to the to the east of Silver City the Martha Washing­ E.-W. fractures cross the stratification and east, but the main channels are N.-S. or N. 15° E. ton, Sunbeam, Undine, Joe Daly, and others - 277,142 34,575,199 appear to have been formed, for the most part, In the Grand Central mine the ore body follows N. 25° to 45° E. directions prevail. - i subsequently to the N.-S. fractures. N.-S. fractures in part, but its main axis is N. 30° Secondary fractures are very rare, the only It is thought that the production of silver and Since the ore bodies follow the fractures, their W., or nearly parallel to the strike and dip of the ones noted being two in the Swansea mines, with gold previous to 1880 did not exceed $2,000,000 general direction is north-south. There are, how­ strata. In the Eagle mine the ore body trends a directions of N. 55° W. and N. 70° E., which dis­ in value. ever, many small ore bodies and por­ few degrees west of north, parallel in strike with place the mineral-bearing veins about 10 feet In addition to the silver and gold, Tintic has tions of large ore bodies which follow the stratification, but with a vertical dip. The each. produced a large amount of lead and copper, the the other fracture directions; but these ore bodies which follow simple N.-S. fractures As the igneous rocks are of Tertiary age, the production for 1898 being over 2,000,000 pounds are subordinate in amount. The fractures which are of much smaller vertical extent than the fractures must be late Tertiary or early Pleisto­ of copper and 29,000,000 pounds of lead. fault ore bodies are very few; and since their Great Mammoth chimney, and are largest near cene. » courses are generally parallel to them, it is only the surface. On the other hand, the top of the ORE DEPOSITION. FRACTURE SYSTEMS. possible to distinguish them as later fractures great ore body in the Grand Central mine seems The fracture systems of the district may be when they actually cross them. The' faulting to have been nearly 1000 feet below the surface. The ore deposits of the region occur along divided into two distinct classes: the first and fractures trend N. 25° E., NE., and E.-W. They The only observed post-mineral fractures in the fracture zones within the sedimentary and igneous more important are those which occur in sedi­ are necessarily of later origin than the minerali­ Mammoth mine trend N.-S. and include an irreg­ rocks and at the contact between the mentary rocks; the second are confined to the zation, and hence than the great majority of the ular band, varying in width from 20 to 100 feet, two. Those in the sedimentary rocks along !rac=te n r» i 11 ture zones. igneous rocks. fractures, but they appear to be older than the vol­ of broken, angular fragments of limestone, which are practically confined to the three Fracturing and mineralization in the sedimen­ canic activity, for in no case have they been traced is popularly known as the " dike." fracture zones above mentioned, the Eureka, the tary rocks occurred before the volcanic activity into the igneous rocks. The E.-W. fractures, G-odwa-8iouw Mountain zone. This begins on Mammoth, and the Godiva-Sioux Mountain zones. and therefore previous to fracturing and mineral­ which occur at the contact of the Robinson quartz­ the south at the North Star, extends NE. to the In the igneous rocks the deposits consist of a ization in the igneous rocks. ite and Eureka limestone, have not intersected east side of Sioux Mountain, thence northward to number of short, widely interspaced veins, with a any known ore bodies, hence their relation to ore Godiva Mountain, and finally NNW. to the north general strike N.-S. and NE.-SW. The principal FEACTUEES EST SEDIMENTARY BOOKS. deposition is not determined. They are undoubt­ side of this mountain. The principal fracture direc­ mines are the Swansea, South Swansea, Sunbeam, Fractures in the sedimentary rocks are very edly older than the volcanic rocks, because in the tions at the south end are N.-S. and N. 25° to 35° Martha Washington, Treasure Hill, Homestake, abundant and may be seen in almost every out­ northern part of the district they have been E.; in the central portion N.-S. and N. 15° E. frac­ and Joe Bowers. The Tintic iron mine, on the crop. They are most readily traceable in the found to stop at the contact. There thus appears tures are more abundant; at the north end N.-S. northern side of Dragon Gulch, has the most con­ quartzites and harder limestones. The Robinson to have been an earlier series of frac­ and N. 15° to 30° W. fractures prevail. They are siderable contact deposit. The more common quartzite is so profoundly sheeted by the N.-S. tures, trending NNW. and NW., which all vertical. The ore bodies follow the fractures; minerals of these deposits are pyrite, galena, fractures as to conceal the bedding in most places. was later intersected by the series of that is to say, they are NNE. at the south end, sphalerite, and enargite and their oxidation prod­ The fractures are most abundant in the vicinity cross fractures trending N.-S., NNE., NE., and N.-S. along the east flank of Godiva and Sioux ucts,' carrying silver and gold, with quartz and of the three great mineral-bearing zones: the E.-W. With few exceptions the displacements mountains, and NNW. at the north end of Godiva barite as gangue minerals. In the sedimentary Eureka zone, the Mammoth zone, and the on these planes do not seem to have been very Mountain. At the south end the ore zone is com­ rocks quartz is the predominant mineral; in the Godiva-Sioux Mountain zone. considerable. They preceded the mineralization; posed of several short ore bodies, while in the igneous rocks the metallic sulphides predominate. The great majority of the fractures occur in but a few fractures are found which have been central portion there is a single ore body which The ores in the sedimentary rocks are mostly the NE. and SW. quadrants, but the most per­ subsequent to the mineralization. has been followed continuously from the Clarissa oxidized down to the greatest depth Depthof sistent are within a few degrees of N.-S. The Eureka fracfavre zone. This zone extends from to the Utah mine, a distance of 5000 feet. Beyond yet mined about 1600 feet below the oxWation- fractures in the NW. and SE. quadrants are less the Gemini mine, northwest of the town of this to the north the bodies are less regular, being surface. In the igneous rocks the ground-water abundant. The fracture planes are nearly verti­ Eureka, through the Bullion-Beck, Eureka Hill, short and lens-shaped, with a pitch south of east. level varies from 200 to 700 feet below the sur­ cal, but in a few cases dip east or west at an and Centennial-Eureka mines, to the Southern In the Northern Spy, Sioux, and Utah mines, in face, being deepest in the Swansea mine. In angle that is rather less than 70°. Eureka, Tennessee Rebel, and Opex mines in the central portion, the ore bodies, which are ver­ these the ore deposits are completely oxidized, There are four principal directions of fracture: Mammoth Basin. In this zone the greatest frac­ tical, or have a steep western dip in the lower above and unaltered below the water level, the N.-S., including variations of less than 10° east or turing has been between the Bullion-Beck and levels, are inclined to depart from the fractures line of separation being very distinct. In the west of the meridian; N. 15° E., N. 25° E., and Eureka Hill shafts. To the south, though nearly at the contact of the Godiva and Humbug forma­ stratified rocks the ores in some cases fill irregu­ E.-W. Of these the N.-S. are the most important as many fractures exist, there are fewer fracture tions and follow the bedding planes of the strata, lar spaces and chambers along the fissure zones; and the N. 15° E. fractures are the Principal_ . . , directions, N.-S. being the most common, and to which dip eastward at angles of from 25° to 65°. in others they replace the country rock. The commonest planes at an angle with fractures- the north there are neither so great a number of Secondary fracturing is slight in this zone and minerals in the igneous rocks, on the other hand, them. The N.- 25° E. and the E.-W. fractures fractures nor so many fracture directions, the is principally seen in the Utah mine, where an occur only within the walls of the fissure planes. cross the stratification and hence are readily principal open spaces being parallel to the E.-W. fault has displaced the ore body. The lead and silver ores predominate almost to recognized. They are apparently later than the bedding planes. The ore bodies follow the frac­ The fact that some of the ore-bearing fractures the exclusion of copper and gold ores at the north­ other fractures. The Spy-Ajax fault, which ture planes in their varying directions. are faulted shows that there must have been two ern end of the various ore zones, as in crosses from Mammoth Gulch to the Northern In the Centennial-Eureka mine their general periods of fracturing. The fractures on either the i (remim/^i ... andI/^IT Goaiva mines, whilei'i ofDistribution metallic minerals. Spy mine, is the most prominent E.-W. fracture, course is N.-S., with minor irregularities. In the side of the Spy-Ajax fault do not correspond, the Centennial-Eureka and North Star, having a displacement of a thousand feet. E.-W. south end of the Eureka Hill mine they also which indicates that this fault was produced sub­ at the southern end of these zones, produce more Tintic Special. 6 copper and gold than lead and silver. Gold, LEAD MINERALS. mines horn silver is constantly found. In the Chrysocolla, varying in color from blue to which is found almost exclusively in the deposits Galena ...... PbS Centennial-Eureka and Gemini mines large masses green, occurs abundantly in irregular masses in Anglesite ...... PbSO4 in the sedimentary rocks, is rarely detectable by Cerussite...... PbCO3 of ore have been mined for their silver content decomposed vein material and country rock. It panning, and hence probably occurs in some Minium...... Pb3O 4 only. Native silver, which has never been a results from a decomposition of all the copper chemical combination. Silver yields the principal COPPER MINERALS. common mineral, is seen only in greatly decom­ minerals mentioned above. values in all the deposits; it is largely in the form Enargite...... Cu3AsS4 posed portions of the ore bodies near the surface. Malachite, occurring in crystals and amorphous of cerargyrite in the deposits of the sedimentary Tetrahedrite...... Cu 8 Sb B S 7 Galena and its oxidation products, cerussite and masses, is abundant as the result of the decompo­ Tennantite...... Cu8AsS 7 rocks, where it coats the breccias of vein material Chalcopyrite ...... CuFeS2 anglesite, are the most abundant metallic minerals sition of the hydrous arsenates and arseniates, and country rock. In the igneous rocks it is Bornite...... Cu8FeS3 of the Tintic deposits. In the Uncle Sam mine especially of olivenite and clinoclasite. Chalcocite...... Cu 2 S found both as cerargyrite and as argentite. The Olivenite...... Cu 3As2O 8 Cu(OH) s hundreds of tons of ore have been mined which Azurite, which is not so abundant as malachite, other minerals of commercial value are lead Clinoclasite...... Cu3Ass O 83Cu(OH) s carry 75 per cent of lead and little or no other is commonly found in crystals attached to solid and copper, the former occurring in both the Erinite ...... Cu3As2 O82Cu(OH) s metallic minerals. It occurs in irregular masses masses of copper sulphides. It is highly prob­ Tyrolite...... Cu3Ass O s2Cu(OH) 3 +7H 2O sedimentary and the igneous rocks, the latter Chalcophyllite.... .7CuOAs2 O 5 . 14H 2 O - associated with pyrite, zinc blende, and quartz. able that malachite is the result of the oxidation principally in the sedimentary rocks. The iron Conichalcite ...... (Cu, Ca)3As2O 8 . (Cu, Ca)(OH) 2 +iH 3 O In the Centennial-Eureka mine it is seen to form of sulpharsenides, and azurite of sulphides of Chenevixite...... Cu2(PeO)2 . As2 O8 +3H 2 O of the contact deposits is valuable, being used for Lettsomite...... 4CuOAl 2 O 3 SO 3 . 8H 2 O the sKell of an ore shoot the center of which is copper. Their occurrence indicates the former fluxing purposes. The bodies of unoxidized ore Brochantite...... CuSO4. 3Cu(OH) 2 composed of enargite and galena. Its association presence of enargite and tennantite in the one found in the sedimentary rocks, and the Origina, form Mixite ...... 20CuO.Bi 2 O 35As2 O 5 . 22H 2 O with quartz and pyrite proves it to be one of the case, and of chalcopyrite and tetrahedrite in the Chrysocolla ...... CuSiO3 4-2H2 O ores exposed in the lower workings ofdep°sits- Malachite...... CuCO 8. Cu(OH) 2 earliest-formed minerals. other. of the igneous rock deposits, show that, in their Azurite ...... 2CuCO 3 . Cu(OH)2 Anglesite, a rather uncommon, colorless mineral, Melaconite, coal-black, without crystalline out­ Melaconite ...... CuO original forms, these ores were sulphides and Cuprite...... Cu2 O has formed in the cavities in the galena as the line, is abundantly present in irregular masses, sulpharsenides, which form 5 to 90 per cent of Native copper...... Cu result of the decomposition of the latter. and results from a decomposition of all copper the ore in the sedimentary rocks and 50 to 80 per IRON MINERALS. Cerussite is the most common form of lead ore. minerals except cuprite and native copper. cent in the igneous rocks. Pyrite...... FeS2 It occurs in aggregations of crystals as well as in Cuprite, resulting from the reduction of melac- Galena and pyrite are the most abundant Scorodite ...... FeAsO 4 +2H 2 O irregular masses without crystalline form. It is onite, is always intimately associated with it, Pharmacosiderite. .6FeAsO4. 2Fe(OH) 3 +12H 2 O metallic sulphides, and enargite is the principal Jarosite...... K2 O3Fe2 O 3 . 4SO 4. 6H 3 O mixed with quartz and jasperoid, and fills cracks merging into it by almost insensible degrees. form of copper as originally deposited. By the Utahite ...... 3Fes O3 . 3SO 3. 4H 2 O and crevices in the vein material and country Native copper in small quantities is found as Borickite ...... Ca3Fe2(PO4)4. 12Fe(OH) 3 +6H 2 O oxidation of the deposits in the sedimentary rocks Hematite...... Fe2 O 3 rock. the result of deoxidation in nearly all the mines. the metals have been separated into ore bodies in Limonite...... 2Fe2 O 3 . 3H 2 O Minium, resulting from the decomposition of A specimen from the Boss Tweed showed a mass which one or the other predominates. Thus, in ZINC MINERALS. other minerals, is occasionally seen. of native copper inclosed by cuprite, and in the the Eureka Hill, Mammoth, Ajax, Carissa, and Sphalerite ...... ZnS ^Enargite is found most frequently in the lower thin sections the transitions from enargite, oliven­ Northern Spy mines large bodies of oxidized cop­ BISMUTH MINERALS levels of the deep mines and in a few of the mines ite, malachite, melaconite, and cuprite to metallic per ore have been found which carried practically Native bismuth... .Bi in igneous rocks near Diamond City. Specimens copper were seen. no lead values. Equally large bodies, almost Bismutite...... Bi2 O 8 CO s H 3 O from the Homestake mine show crystals of enar­ Pyrite is rare in the sedimentary rocks because exclusively of lead ore, occur in the Eureka Hill, SULPHUR. gite fully one-half inch in length. The minerals of the thorough oxidation of the deposits. It is Bullion-Beck, Utah, Sioux, and Mammoth mines, Native sulphur .... S observed in the sedimentary rocks are in crypto­ occasionally seen in the small patches which are while large amounts of cerargyrite were taken Quartz is always present in these deposits, fre­ crystalline masses which are always coated with coated with iron oxide, except where it has from the Gemini mine. Such ore bodies occur quently occurring in great masses in the lime­ oxidation products and sometimes contain chal- resulted from the decomposition of copper sul­ filling caves, or in zones of brecciated vein- stone, but with so little of the metallic minerals copyrite. phides. It is certain from the great amount of material or country rock adjacent to the original as to be of no commercial value. It occurs either Chalcocite, like bornite, is an uncommon min­ iron oxide now present that pyrite was at one time ore bodies. in crystals or crystalline masses deposited in open eral and results from the decomposition of tetra- a very abundant mineral. In the igneous rocks, In structure the original ores are either massive spaces or in cryptocrystalline masses replacing the hedrite, chalcopyrite, or possibly bornite. where the water level is near the surface, the or banded, or imitate the texture and color of country rock; it has been deposited at various Olivenite, one of the first products of the oxida­ pyrite is well preserved and can be seen dissemi­ the inclosing rocks. Banded structure, structure of intervals during the mineralization, and has also tion of enargite, occurs in hair-like crystals, which nated throughout the veins and impregnating the found in both the igneous and the sedi- originalores- been found as a secondary deposit formed subse­ shade from pale to dark olive-green, and also in country rock near them. It also occurs frequently mentary rocks, is due to variations in the amount quently to the oxidation. Microscopically the compact, fibrous, wood-brown masses. It forms in large lens-shaped bodies of almost solid pyrite, of silica deposited. In the deposits in the sedi­ individual crystals frequently show enlargement. around masses of enargite, or lines cavities in especially near the ground-water level. mentary rocks massive and pseudomorphic struc­ Cases have been observed where the quartz lines altered limestone. It is often coated with other Scorodite occurs in crystals varying from lake- tures are the more common. cavities in galena, and on the walls; it has been copper minerals, with calcite, or even with quartz. green to olive-brown; it is amorphous and earthy. Contact deposits occur on or directly connected found coated with barite, to which, in turn, Clinoclasite differs from olivenite by its crystal Pharmacosiderite is found in brown cubic with the contact of the igneous rocks with lime­ younger quartz crystals cling. Quartz which was form and its very uniform dark bluish-green color. crystals attached to rusty quartz. In color it is

stone,7 and are,' for the most part,r i Contact_ . . plainly more recent than the oxidation has been The crystals sometimes produce a rough, shining, straw-yellow and pale green. The crystals are so replacements of limestone along this dep°sits- seen coating crystals of calcite and the rough plated surface, as they frequently group them­ small that it is often overlooked or confounded contact. Mineralization has formed great masses surfaces of copper carbonates. The cryptocrys­ selves in radial clusters. Its association and mode with jarosite and scorodite. of siliceous material impregnated with hematite talline masses of silica which replace the lime­ of occurrence are the same as those of olivenite. Jarosite occurs in druses of minute crystals in and limonite and containing locally small amounts stone preserve its texture and color and often jffrinite, which is dark emerald-green in color, clusters or as an incrustation. In color it is of the precious metals. They consist principally contain irregular patches of carbonate of lime or occurs in hair-like groups of crystals lining cavi­ yellow or clove-brown. of jasperoid, or silicified limestone. A typical magnesia. Chalcedonite is, on the whole, rare. ties and closely associated with enargite, azurite, Utahite forms in fine orange-yellow scales exposure may be seen on the southwest slope of It occurs in intimate association with the quartz, and clinoclasite. which have a soft, silky lustre. It is found in the Mammoth Peak, near the new East Tintic Rail­ but can not be distinguished from it without the Tyrolite is of a very brilliant green color, inten­ Eureka Hill, Bullion-Beck, Mammoth, and Ajax way, where great masses of silicified rock project aid of a microscope. sified by its mica-like cleavage and radial struc­ mines. from 15 to 20 feet above the surface. The jasper- Barite, next in importance to quartz, was one ture. Borickite is a compact, massive mineral with­

oid is similar in every > respect* to the Jasperoid, of the earliest minerals to form in the deposits in Chalcophyllite is found in the form of small out cleavage. Its lustre is waxy and its color cryptocrystalline quartz which occurs reP!acement- the sedimentary rocks; it is quite generally dis­ hexagonal plates arranged in rosettes differing reddish brown. in the other deposits of the district. It contains tributed through them. In the Carissa mine it from the radial structure described for tyrolite. Hematite and limonite are common to the oxi­ also spots and small masses of unreplaced lime­ forms a nearly solid body almost 25 feet wide, 40 Its color is bright apple-green with pearly luster dation zones of all the deposits. They result stone and dolomite. It so closely imitates the or more feet long, and 50 feet in vertical extent. and it has marked cleavage. from the alteration of pyrite, and, to a small structure of the rock it replaces that fre­ Calcite and dolomite form residual spots and Chenevixite is a compact, greenish, opaque extent, from the decomposition of other copper quently it can be distinguished from the latter irregular patches throughout the cryptocrystalline mineral scattered in irregular patches throughout minerals which contain iron. Neither limonite only by its hardness and its failure to effervesce. quartz representing, presumably, unreplaced por­ portions of Ore that occurs in hard lumps, and nor hematite were originally deposited as such, it The contact deposits always carry a considerable tions of the country rock. There has also been gives a mottled appearance to a broken surface. is thought, except possibly in the contact deposits amount of hematite and limonite, and in the much secondary calcite deposited in open spaces, Its color is olive-green, shading into greenish yel­ in the Tintic iron mine. They occur in irregular Tintic and Black Stallion iron mines these have whatever be the nature of the inclosing rock. In low after exposure, with little or no luster. masses and in minute particles in all portions of been found profitable to extract. The iron ore frequent instances oxidized ores are found coated Conichalcite, in color varying from pistachio- to the oxidized zone. In the Ajax mine a large cave of the Tin tic iron mine contains about 80 per with calcite. emerald-green, strongly resembles malachite. It was found across which extended at various cent of iron oxide, 14 per cent of water, and 3 Selenite forms as the result of the oxidation of is reniform and massive, coating surfaces with angles hollow diamond-shaped rods of limonite per cent of silica, with very small amounts of the sulphide ores in the presence of the limestone decomposed copper arseniates. from which hung stalactites. The form of the alumina, lime, magnesia, and sulphuric and phos­ country rock. Lettsomite (cyanotrichite), from the Ajax mine, open space in the rod and an occasional corroded phoric acids. Gold, on account either of its finely divided occurs in druses, forming a velvety lining of short mass of gypsum showed that the cave must have state or of its chemical combination, is rarely capillary crystals, sometimes like spherical glob­ been crossed by numerous long, slender crystals MINERALS OF THE ORE DEPOSITS. revealed by panning. The richest gold ores inva­ ules. Its color is a clear smalt-blue, sometimes of the latter mineral. riably contain a large amount of barite in minute passing into sky-blue. Sphalerite, or zinc blende, was found in the Quartz...... SiO s Chalcedonite ...... SiO2 crystals. Tellurium has been found in the ores, Brochantite occurs in two distinct forms: (1) Swansea mines in association with pyrite and Barite ...... BaSO4 but it is not certain that the gold was originally in the ordinary form, with prismatic habit, the and galena. It is an original mineral which has Calcite ...... CaCO, Dolomite...... MgCO 3 all in the form of telluride of gold; some may transparent crystals having a dark-green color; (2) been but little altered. It is usually without Selenite ...... CaSO4 have been associated or combined with the large with curved double wedge-shaped crystals, light crystalline outline, is resinous yellow in color, amount of pyrite which originally existed in the green in color; the crystals do not exceed 2 or 3 and shows characteristic cleavage. GOLD MINERALS. ore. millimeters in length. Native bismuth, in very delicate crystals, was Native gold...... -Au Argentite and stephanite occur occasionally as Mixite occurs in pale bluish-green hair-like crys­ found in the Emerald and Boss Tweed mines in SILVER MINERALS. minute grains or crystalline inclusions in the tals, arranged in radial clusters, and often forming perfectly fresh limestone apart from any known Stephanite...... Ag5 SbS4 galena ore. Cerargyrite, or horn silver, forms a very soft, velvety coating on tabular crystals ore deposit or vein. On account of the smallness Argentite...... Ag2 S Cerargyrite...... AgCl films and crystals coating the fragments of vein of barite. It is associated with olivenite and bis- of the crystals its determination rests upon analy­ Native silver...... Ag or country rock. In the oxidized zones of all the mutite. sis. 7

Bismutite is associated almost exclusively with changes a rock containing 75 per cent carbonate The outcrops of the"ore bodies give no idea of ing the limestone it is probable that there has been quartz and barite. It is a grayish straw-colored of lime to one carrying nearly 85 per cent of silica. their size. In the Bullion-Beck mine a chemical reaction between the components of mineral without crystalline form. Mechanical alteration in the igneous rocks has it was said that no ore was encountered not ah?a?sdo the vein solutions and the carbonates of lime and Native sulphur was found in crystals coating been confined almost entirely to the more compact^ until the workings reached a depth of magnesia of the wall rocks. Deposits forming in cavities in massive galena ore. In the Eureka granular rocks, and in no case has a 80 feet. In the Gemini, ore was struck only preexisting spaces, whether in sedimentary or in Hill mine some of these crystals, one-eighth of an large fissure been found. No shearing in ignaedu" below the 400-foot level. igneous rocks, may be the result of chemical pre­ inch in diameter, w^ere nearly perfect. Its mode or granulation of the individual miner­ The average value of the ore appears to be cipitation due to loss of temperature or of pressure, of occurrence, coating cavities and attached to als of these rocks was observed. Chemical alter­ decreasing, a fact which is due rather to the pass­ or to changes brought about in the solutions upon known products of oxidation, indicates its origin ation is confined in these rocks to the few inches ing from the totally oxidized ores, which have mixing with surface waters containing oxygen, as a part of that general process. next to the veins and to the contact of the sedi­ become richer in the process of oxidation, to the carbonic acid, or organic matter. Order of deposition. Microscopic study shows mentary rocks. It has produced quartz, pyrite, less oxidized, than to an actual decrease in the The structure and composition of the contact that quartz is formed almost continuously from and sericite in the wall rocks next to the veins. value of the original ore. deposits indicate a different method of formation. the beginning to the end of the process of miner­ Pyrite occurs both as an impregnation of the Ore bodies in igneous rocks. In the igneous It is probable that they were formed alization, that it frequently replaces limestone, country rock and as a filling of microscopic cracks. rocks the ore bodies vary from a mere seam to comparatively near the surface by ofeoriginaige and that some of it has been formed subsequent Quartz and sericite appear to be the result of the veins 10 feet in width. Their limits are always thermal11 springs. Or/-VPT these threei lormsr» deposits. to the oxidation. Barite is earlier than the metal­ alteration of the original rock, the former having well defined, though clay seams or friction brec­ of deposits, those in the sedimentary rocks are the lic minerals. The metallic minerals were all been seen to replace certain of the feldspars. cias separating ore from country rock are rare. oldest, as shown by the facts that they are cut off deposited about the same time, but later than the Ore bodies in sedimentary rocks. The ore bodies The most continuous ore body is the Sunbeam by the igneous rocks, that fragments of their vein earliest quartz and the barite. In the Boss of the sedimentary rocks are found along nearly vein, which is 2000 feet long; the majority of material are found in the talus, which in some Tweed mine quartz was found in distinct crystals vertical fractures, and extend into the country the veins are not more than a few hundred feet cases separates the sedimentary from the igneous containing hexagonal skeletons of a finely divided rock on both sides for from a few inches to more in length. As in the sedimentary rocks, the ore rocks, and that portions of these veins are found dark mineral. It was also seen in irregular than 50 feet. These bodies are extremely irregu­ follows mainly N.-S. or NNE. fissures. The in the contact deposits. The evidences of the masses inclosing malachite and chrysocolla and lar and are seldom bounded by definite walls, so veins of parallel and adjacent fractures do not relative age of the deposits in the igneous rocks lining druses in soft, decomposed vein material that the change from ore to country rock is vague overlap and are generally connected by ore- and those along the contact are not conclusive. and country rock. In the Eureka Hill mine in and must be determined either by assay or by the bearing cross fractures, the cross fissures being Deposits in the igneous rocks are composed of one case quartz was found coated with and coat­ hardness of the rock, the silicified limestone being barren beyond the intersections. sulphides, while the latter are oxides. The fact ing both sulphides and oxidation products. In invariably harder than the unaltered. There is a marked banding in the ores, pro­ that these oxides may have been derived from another case fine-grained quartz was seen lined The ore bodies follow, for the most part, N.-S. duced by -the varying proportions of the minerals. secondary sulphides in the neighboring eruptive with coarsely crystalline quartz containing crys­ fissures, but fissures of all directions have been The bands containing the greatest amount of rocks is suggestive of a more recent age for the tals of barite. Upon the latter quartz formed found between N.-S. ore bodies. The ore bodies galena constitute pay shoots. Individual bands contact deposits. subsequently ; some of it was highly altered and rarely branch or split. When two fissures meet, are sometimes separated by clay seams. The pay Secondary deposits. In both sedimentary and coated with still more recent quartz. Quartz the ore body is usually larger at the intersection shoots are lens-shaped and without definite pitch, igneous rocks the surface waters have oxidized pseudomorphic after calcite occurs in the Mam­ if the vein continues its course beyond the point though their longest axis is usually horizontal. the ore bodies, leached the deposits, and rearranged moth, Centennial-Eureka, and Bullion-Beck of intersection than if it departs on the intersect­ While there is a marked decrease in value from the various minerals, forming new chemical com­ mines. ing fissure. the oxide to the sulphide ores, and the veins are binations among the metals. By this process the The vertical extent of individual ore bodies is never large, still there is no good reason for believ­ metals have been separated into distinct ore bodies, GEOLOGICAL EELATIOISTS OF DEPOSITS. rarely more than 200 feet, though a large shoot ing that they will not persist to a much greater which occur in open spaces in the vein and country

Rock alteration. The changes in rocks due to in the Eureka Hill mine has a lengthO Extent_ , . of. ore depth than that at which they are now worked. rock, made since the original mineralization. In fissuring and vein formation are either mechanical of 600 feet, and another in the Mam- bodies- Contact deposits.- In the limestone, along its the sedimentary rocks these deposits extend to a or chemical in their nature. moth mine of 1600 feet. Small horizontal pipes contact with igneous rocks, either monzonite or depth of 1500 feet; in the igneous rocks to 200 Mechanical alteration in the sedimentary rocks are common in all the mines. The longitudinal rhyolite, occur bodies of jasperoid which contain or 300 feet. has caused the sheeting of the more resistant extent of the ore bodies is as variable as the ver­ in places sufficient iron to render the ore valuable In this process the pyrite, galena, and enargite strata, such as quartzites, and the brec- tical. Those bodies which occupy strong frac­ for fluxing purposes. The most important depos­ have been changed to limonite, cerussite, and ciation j_* 01j? thej.i limestonei j. and111 dolomite, ' L Alterationsedimentary in tures having a definite angle with the planes of its are, first, the Tintic iron mine, which is situated cerargyrite, respectively. The enargite has passed An unusual example of brecciation stratification are more continuous than those south of Mammoth Mountain, on the contact of through various forms of hydrous arsenates and found in the Mammoth mine is locally known as which occur in openings that result from the Eureka limestone with monzonite; and, second, arseniates into the oxides of copper and native "the dike." It is a large mass of greatly brec- slipping of individual beds on one another. The those on the first ridge east of Mammoth Moun­ copper. The alteration has been effected by sur­ ciated limestone which can be traced on the sur­ longest observed ore body extends from the Utah tain, just beyond the border of the area mapped, face waters carrying atmospheric oxygen, organic face and below it for many hundreds of feet. It to the Carissa mine, a distance of 5000 feet, while along the contact of rhyolite and Eureka lime­ matter, chloride of sodium, and phosphoric and is of so recent origin that the fragments are with­ in the Bullion-Beck and Gemini there are many stone on which is situated the Black Stallion carbonic acid. The separation of the minerals of out calcite or secondary mineral cement. ore bodies not more than 25 feet long. group of mines. The rocks on either side of the the originally complex ore bodies into deposits It is along the channels produced by mechan­ There appears to be no definite order in the contact have been extensively altered, the altera­ containing only one of the various metals is prob­ ical alteration that the chemical changes have distribution of the richer portions of the ores. tion taking the form of replacement of the lime­ ably due to difference in stability and solubility taken place. Chemical alteration in the sedi­ The smaller ore bodies average higher generally stone, while in the monzonite the feldspar has of the original minerals, though the changes mentary rocks has affected the walls of the fissures than the large ones, and it has also been found been changed to sericite. through which these original minerals have gone by replacing them with silica, galena, and some, that the ore is richer where the ore body widens Origin of deposits. Deposits in the sedimentary have probably been an important factor in the possibly all, of the other minerals of the vein at the intersection of two fissures. The greatest and in the igneous rocks were probably made by final separation. deposits. The commonest change is the substitu­ depth of ore mined at the present time is in the ascending heated waters carrying hydrogen-sul­ GEORGE WARREN TOWER, JB., tion of silica for lime. This process does not Bullion-Beck, where the workings have reached phide, alkaline sulphides, and arsenical sulphides, Geologist. affect the original structure, texture, or color of a depth of 1600 feet (about 4750 feet above sea with some forms of silica, barium, lead, copper, the rock, but chemical analysis shows that it level). silver, and gold. Where ore bodies occur replac- November, 1899.

GENERAL CONCLUSIONS. folding, for the reason that a great number of the them and those of the igneous rocks. It might eruptions, afforded a great depth of run-off to fractures cross the bedding at a low angle either be assumed to indicate that the latter do not surface waters, and hence favored the formation A review of the facts gathered by Messrs. in strike or in dip. A certain amount extend through these rocks into the I underlying of caves in the mass of the limestone strata. Smith and Tower in their geological study of the of slipping; on bedding planes may iatsesruthan sedimentary rocks ; hence that they a|re likely to Nevertheless, there does not appear to be any i, A ^ 5 i*i- i, * -\ folding- Tintic special district leads to the following have accompanied the lolding, but it be found of less extent in depth. definite evidence that the original deposits in general conclusions with regard to the economic seems probable that such as caused a buckling or Contact deposits. The contact deposits prob­ limestone at Tintic were cave deposits. They are geology of the district. bending apart of adjoining strata, sufficient to ably do not owe their existence solely to the fact mostly replacement deposits, and, in some cases, Age. It ^ seems well established by the evi­ _ leave a space for the accumulation of ore, must of their occurrence at the contact of Contact de= the filling of open spaces formed by dynamic dence obtained that the original deposition in the have been caused by later dynamic movement. limestone and igneous rocks, but their movement or fissuring. A large proportion of sedimentary rocks occurred previous to the erup­ If the assumption is correct that the fissuring in concentration at the observed points flssunng% the actually existing open caves occur tion of the igneous rocks, but in the usually oxi­ the igneous rocks was accompanied by a renewal was probably due to some fissuring which admit­ over oxidized ore bodies and evidently reult'not , . . , ~~ the cause, of dized condition of these deposits one can not be of movement in the fracture zones of the sedi­ ted the mineralizing solutions and from which owe their existence to the settlingts to oretion. deposi­ sure that additional mineralization has not subse­ mentary rocks, it is probable that the fissures in they spread out into and replaced the adjoining the bottom of the material of a large quently taken place in the sedimentary rocks, the latter now extend to a considerable depth limestone. Further, there does not seem to be ore body. It is well known that in the oxidation and possibly at the time of the ore deposition in and are not likely to decrease in value with any final proof that they were originally deposited of a body of sulphides which has replaced lime­ the igneous rocks. There has undoubtedly been depth, except as a change from enriched oxides as oxides. It is not improbable that they may stone there is a removal of a certain part of the a later shattering or fissuring of the Secondar to sulphides and arsenides, until the fractures have been deposited as sulphides at or near the constituents, and it is possible that the original sedimentary rocks since the formation flssurin«- have passed into the underlying quartzite at the present location of the limonite ores, and, by sulphide replacement was accompanied by a of the original fissures, and it may reasonably be bottom of the supposed synclinal basin. the action of thermal springs, have since been slight contraction of the mass. The former is, assumed that this took place at the time of the Ground-water level. The remarkable differ­ altered to hydrous oxides and more or less trans­ however, the more important operation from the formation of the fissures in the igneous rocks that ence in the level of the ground water in sedi­ posed. present point of view. It leaves the mass in a have since become mineral-bearing veins. It is mentary and igneous rocks is signifi- Signlficance Cave deposits. Cave deposits constitute an porous condition, somewhat in the nature of a noteworthy that the latter have a similarity in cant, but its interpretation is not in jJgSSS,11 unusually interesting and important feature of loose aggregation of sand grains, which would be general direction and relative position to the every respect clear.i ItTJ_ is in so tar£ a water level. the Tintic ore bodies in limestone. The great the less coherent the greater the amount of leach­ older fissure zones. confirmation of the induction that the fissures in elevation of the limestone mass above the bottom ing to which it had been subjected. A shaking The original fissuring in the sedimentary rocks the sedimentary rocks are the older, since it of the surrounding valleys, which must have up of the mountain mass, such as must have is assumed to be mainly of later date than the shows that there is no present connection between been even more marked previous to the igneous accompanied the formation of what is called the Tintic Special. 8

" dike" in the Mammoth mine, would have waters. Hence, where a rich body of oxidized be found to be richer and more extensive than detected all that exist within the oxidized zone, loosened and caused to settle to the bottom the ore is found, its continuation should be looked those in the igneous rocks. Their secondary and further explorations may, therefore, prove less coherent material, leaving an open space or for above as well as below, for it is evident that alteration, and consequent local enrichment, has^ remunerative. cave above, just as would be occasioned by the where during oxidation there has been a transpo­ been unusually extensive, and it may naturally In depth there seems to be no valid reason to shaking down of sand in a loosely filled glass sition of valuable metals, it would be downward be expected that when the entirely unaltered expect that 1/he ore bodies will be found to be less tube. In the cave in the 1300-foot level of the rather than upward, and the distance to which deposits are reached they will be found to be extensive or less continuous than they have been Mammoth mine, for instance, portions of the ore they would be carried would bear some relation on the average less rich than those that have in the ground already explored, at least within are seen to be still clinging to the roof of the to the relative solubility of the sulphates of the already been worked. Still, there is no definite the probable limits of profitable exploitation. cave. Other caves which are now filled by strati­ respective metals, evidence that the lower limit of secondary SAMUEL FRANKLIN EMMONS, fied material are probably of similar though per­ Futwe explorations. It may be assumed that enrichment has been reached, and as the valuable Geologist. haps earlier origin^ but have been filled by mate­ in the future, as has been the case in the past, ore bodies do not always outcrop at the surfacd, rial washed in from above by downward-seeping the ore bodies in the sedimentary rocks will it may well be that present workings have not , January, 1900.