OFR 5-89 - Alaska Resources Library & Information Services (ARLIS)

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TIN OCCURRENCES General Description The Ohio Creek pluton contains tin-, silver-, and base-metal-bearing quartz-tourmaline and quartz-muscovite5/ greisen.§ occurrences 5/Muscovite in this report refers to a generic pale mica of unknown composition. 6/An altered rock of generally granitic composition composed mostly of quartz, mica, chlorite, topaz, fluorite, or tourmaline and associated with ore minerals of tin, tungsten, and molybdenum. along the contact between an argillite inclusion and muscovite granite in the northwestern portion of the intrusion. Tin-mineralized quartz-muscovite greisen-bordered arsenopyrite veins are also present in the structurally higher portions of the pluton. Wolframite- [(Fe,Mn)W04] bearing quartz veins within both the argillite country rock and the muscovite granite area are also locally present. Figure 3 is a detailed geologic sketch map of a hornfelsed argillite inclusion and associated greisen located in the northwestern portion of the Ohio Creek pluton (fig. 2). The inclusion is partially exposed along approximately 300 ft of creek length and dips steeply to gently northwest, subparallel to the orientation of original bedding in the argillite. Massive fine-grained to vein-like coarse-grained quartztourmaline and quartz-muscovite greisen are locally present in the muscovite granite along its contact with the argillite inclusion, and in granite dikes or sills within the inclusion. The inclusion is cut by unaltered, northwest-trending steeply north-dipping shear zones. Cassiterite-bearing 0.1- to 1.3-ft-wide arsenopyrite-quartz veins are common within an approximately 1,000-ft-long and up to 50-ft-wide, iron-stained area near the upper contact of the pluton and are also locally present near the southeastern margin of the Ohio Creek pluton (figs. 2, 4, and 5). The veins strike north to northwest and dip moderately to steeply northeast, subparallel to the pluton's upper contact. Where most closely spaced, the veins occur at intervals of approximately 8 ft over a width of approximately 50 ft (fig. 4). In the upper portions of the pluton, the arsenopyrite-quartz veins have quartz-tourmaline and/or quartz-muscovite greisen selvages that are especially well-developed in the footwall. The width of the vein and selvage, together, ranges up to 2.5 ft, but averages approximately 1.5 ft. Trace to minor amounts of chalcopyrite, pyrite, sphalerite, and galena, as well as cassiterite, are locally present in the arsenopyrite veins or their greisen selvages. Cassiterite was observed associated with arsenopyrite and occurred as up to .5-cm dark brown euhedral grains in several veins. 7
Tgrn~~~~~~~~~~Tr Tgm ~ ~ Tg fig / \ \ / - A r ge a d h r t s /~ ~ ~ j/ ~~g /J Ag( 55/ ~ g /j X +f>bGN -. 5~ -^N/-. 52 5'57 A0 '00 E Oat-ormln A 0 ;0 20 40 m -g - i Scale, it - Strl aContours approximate rle Arg - *66 Arg ~~~~~~~~~~~~~~~~~~~~~~~~~muscovite granite S-.- A / f~~- - - ., Xt -' t o soI ? jt Ih~°eprnia~t hr LEGEND Arg Argillite and hornfes Fuartz-tourmaliCr e grelsen W uartz~tmuscovite greisen 2' .- Geologic contact, showing dip, dashed where approximate, dotted where Interred, queried where uncertain Shear zone, showing dip, dotted where JgM ~~~~~~~~~~~~~~~~~Inferred, queried where uncertain 50 Strike and dip of bedding 6 11-~ Channel sample 5 1 * Sample location Figure 3. -Geologic sketch map of the hornfelsed argillite inclusion, northwestern Ohio Creek pluton
Page 1 and 2: TIN OCCURRENCES ASSOCIATED WITH THE
Page 3 and 4: cm ft lb mm m.y. oz/st pct pH UNITS
Page 5 and 6: This report describes a portion of
Page 7 and 8: course of field studies, 3 bulk sam
Page 9: TABLE 1. - Major oxide analyses 11
Page 13 and 14: 1E Muscovite granite .*.-62 LEGEND
Page 15 and 16: Concentration Testing After separat
Page 17 and 18: TABLE 2. - Size distribution of the
Page 19 and 20: TABLE 4. - Metallurgical balance fo
Page 21 and 22: TABLE 6. - Metallurgical balance fo
Page 23 and 24: C. 0 .1 .2 .4 .5 mmm .3 (a) (C) Q Q
Page 25 and 26: only 33 ppm Sn. Samples of the quar
Page 27 and 28: APPENDIX A - Results of sample anal

OFR 5-89 - Alaska Resources Library & Information Services (ARLIS)

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