CONTACT INFORMATION Mining Records Curator Arizona Geological Survey 416 W. Congress St., Suite 100 Tucson, Arizona 85701 602-771-1601 http://www.azgs.az.gov [email protected] The following file is part of the Grover Heinrichs Mining Collection ACCESS STATEMENT These digitized collections are accessible for purposes of education and research. We have indicated what we know about copyright and rights of privacy, publicity, or trademark. Due to the nature of archival collections, we are not always able to identify this information. We are eager to hear from any rights owners, so that we may obtain accurate information. Upon request, we will remove material from public view while we address a rights issue. CONSTRAINTS STATEMENT The Arizona Geological Survey does not claim to control all rights for all materials in its collection. These rights include, but are not limited to: copyright, privacy rights, and cultural protection rights. The User hereby assumes all responsibility for obtaining any rights to use the material in excess of “fair use.” The Survey makes no intellectual property claims to the products created by individual authors in the manuscript collections, except when the author deeded those rights to the Survey or when those authors were employed by the State of Arizona and created intellectual products as a function of their official duties. The Survey does maintain property rights to the physical and digital representations of the works. QUALITY STATEMENT The Arizona Geological Survey is not responsible for the accuracy of the records, information, or opinions that may be contained in the files. The Survey collects, catalogs, and archives data on mineral properties regardless of its views of the veracity or accuracy of those data. 40 IGNEOUS ROCKS AND RELATED MINERAL DEPOSITS OF THE BARKER QUADRANGLE, MONTANA MAFIC ROCKS 17 ~i= '----.J'---'-----'--~ch'-=-----."'! a: EXPLANATION o z Minette-kersantite l >- 0:: « f- 0:: Rhyolite of Granite Mountain W f- ~..... Tb · ~ Barker Porphyry UNCONFORMITY z « Il.. s... .0.. Il.. ~ .~~ { Lower partCIEEJ of Madi son Group til j .~ UNCONFORMITY til UJ ~ til ~ A C Three Forks Formation z « z 0 J efferson Dolomite > W 0 Maywood Formation UNCONFORMITY Pilgrim Limestone 4 --- z « 0:: B m Park Shale «~ u Older Cambrian units I I- '«::::J 0- 0 0 0 0 0 0 (1) 8 0 0 0 0 0 0 ... 0 <0 N 00 0 r-- r-- <0 <0 ... "' "' "' Contact, approximately located U o Fault, approximately located U, upth,-own side; D, downth"own side 14 --'-- B D Strike and dip of beds FIGURE 7.-Intermediate and mafic igneous rocks from the clase grain jacketed by alkalic feldspar enclosed in a micro­ Barker quadrangle. Scale of both hand specimens in centi­ o 1'2 MILE granular groundmass. C, D. Shonkinite. C, Hand specimen. I I meters. Photographs by R. B. Taylor, Sandra Brennan, and Dark-gray to black mafic rock marked by medium- to CONTOU R INTERVAL 200 FEET Louise Hedricks. A, B. Barker Porphyry. A, Hand speci­ coarse-grained texture. Large dark-gray to black partly men. Light-gray quartz latite porphyry characterized by rounded minerals are olivine. D, Photomi~rograph showing FIGURE 23.-The west flank of the Granite Mountain bysmalith. Base from U.S. Geological Survey, Mixes Baldy quadrangle, angular white laths of feldspar and black needles of horn­ ovoid olivine grain broken by curving fractures and en­ 1 :24,000, 1961. blende and flakes of biotite in a fine-grained groundmass. circled by biotite flakes. B, Photomicrograph showing sanidine, quartz, and a plagio- 18 IGNEOUS ROCKS AND RELATED MINERAL DEPOSITS OF THE BARKER QUADRANGLE, MONTANA INDURATED ALLUVIUM 39 SPECIMEN NUMBER santite, composed of biotite, orthoclase, and plagio­ clase; and (5) vogesite, similar to the minette-ker­ 00 N ~ santite, but including much pyroxene or hornblende (table 3). Petrographic details and modal and chem­ ical analyses of these rocks are given in table 4. Contact between laccolith (left) o 5 The mafic rocks do not seem to be distributed at Barker Mountai and Madison strata (right) & ~ random. Most of the shonkinite, plagioclase shonkin­ '" ~ 4 "' + ite, and syenite crops out in the northwestern part Cl) ~ ~O 3 ro iJ' of the Barker quadrangle (closer to the shonkinite­ ~~o - f- 2 rich Highwood Mountains); most of the minette- EXPLANATION 5 ,--------------------------------, o Barker <) l1 nilrangie 4 • Ne ih art quadrangle 3 6 0 o 0 [). Stanford· Hobson area :g"" 2 o o FIGURE 22.-View looking westward from Mixes Baldy at chiefly the Pilgrim Limestone. Heavily wooded area in o L-______________________________~ the north and east flanks of Barker laccolith. The north­ left foreground is part of the west edge of Hughesville east flank of the laccolith is in intrusive contact-possibly stock. Rockslides in right foreground are part of the de­ 5 ,--------------------------------, as a result of a preexisting fault-with Madison strata, 3 nuded southwest end of the Clendennin-Peterson laccolith. 8 9 ' 4 0 whereas all other flanks pass below Cambrian strata, Irene Peak is the upturned edge of a resistant sill. 4 6 " --BI O~2 (0 16 15 I) fti:::19 ~ 3 I P~OcJg\1 2 U ) 4 18 2 of about 5,750 feet. Here the indurated alluvium ex­ as 6 inches in size and rather well rounded, are tends down to and passes beneath the valley floor; incorporated in other masses of indurated alluvium. Na,O K,O the altitude of its base is unknown. If, however, the The deposits were clearly laid down by streams. gradient of modern Gold Run Creek, 100 feet to the Iron mile, is accepted as the gradient of its ancestor, then The indurated alluvium includes poorly sorted an­ the altitude of the base of the indurated alluvium in gular to subrounded cobbles of Wolf Porphyry, of this locality can be calculated to be about 5,600 feet. the porphyry of Olendennin Mountain, and of the The 150-foot difference between exposed top and quartz monzonite of Hughesville. In these cobbles, calculated base is probably an average thickness for many of the feldspars have been intensely altered to the indurated alluvium. It seems doubtful that the white clay. Grains and seams of pyrite and chalco­ alluvium exceeds 200 feet in thickness. pyrite are in fragments of both the quartz monzon­ ite of Hughesville and the Wolf Porphyry. Commonly, the indurated alluvium stands as a steep or nearly vertical wall, and is veined by man­ The matrix invariably is brown and consists of a 60 62 64 66 68 70 ganese-stained fractures. Loc3ilIy, steeply tilted SiO,. IN PERCEl'JT motley of fine to coarse particles more or less blocks of the alluvium, 50-100 feet across, are en­ cemented by silica and limonite. Much of it consists EXPLANATION closed in the main mass and invariably dip toward of minerals derived from the disintegration of the the embankment. These features suggest that they Wolf Porphyry, of the quartz monzonite of Hughes­ o Hug hesville stock are slide blocks. vj,]]e, and of various metamorphic rocks. As a result, o L a ccoliths In most exposures the indurated alluvium is a round and angular quartz grains (from the Wolf(?) [). Sills MgO Na,O +K, Q light-brown to grayish-brown, firm, well-cemented Porphyry), as well as altered alkalic and plagioclase jumble of angular to well-rounded rock fragments feldspars (from the quartz monzonite.), are which range in size from a quarter of an inch to 1 common. Small amounts of garnet (from the meta­ FIGURE S.- Silica variation diagrams for intermedi­ FIGURE 9.-Comparison of some chemical characteristics of ate rocks from both large and small intrusions the intermediate rocks from the Barker quadrangle with foot; most, however, are about half an inch long. A morphic rocks) are present. Small specks of pyrite scattered through the Barker quadrangle. The comparable rocks from the Neihart quadrangle and from few beds are composed of moderately well sorted are also s·cattered irregularly through the matrix. grouping indicates that the intrusions came the Stanford-Hobson area. See table 2 for sample loca­ sand and pebbles; crossbedding is common; and here Mafi·c minerals are rare, presumably because most from the same magma. Specimen numbers are tions, and Vine (1956, p. 454-455) for location of samples and there cobbles of the' indurated alluvium, as much have been weathered and removed. identified in table 2. from the Stanford-Hobson area. 38 IGNEOUS ROCKS AND RELATED MINERAL DEPOSITS OF THE BARKER QUADRANGLE, MONTANA MAFIC ROCKS 19 TABLE 3,-Lamprophyre t erminology PLAGIOCLASE SHONKINITE (Sample 2 of table 4) Dominant f eldspar Several minor plagioclase shonkinite intrusions around Barker Mountain are indistinguishable in Orthoclase Plagioclase hand specimen from the shonkinites; their greater plagioclase content is apparent only in thin section. .2l The plagioclase feldspar is albite (An5_ 7 ), and it :;:; Minette Kersantite " 0 dominates the mineral assemblage. It forms elongate ""s'" iii ..,.. laths that are enveloped by alkalic feldspar. " '" Many of the olivine grains have been altered to a 'S" ~~ 0 "'.c ~ >< ", Vogesite Spessartite fibrous mesh of alteration products, which (because g S they probably include both antigorite and chryso­ Po."''' k 0 tile) are here grouped as serpentine. kersantite and vogesite is in the southern half. I am SYENITE uncertain whether this pattern has more than local (Samples 3- 5 of table 4) significance, inasmuch as shonkinite is also exposed A few thin syenite sills are interlayered in the to the south at Yogo Peak (Weed, 1900, p. 397) sedimentary units of the Big Snowy Group exposed along the valley walls of both Little and Big Otter Creeks. And several more are exposed in the steeply SHONKINITE tilted beds that form part of the nose of the Clen­ ~w " \,.