Llano-Burnet Region, Texas With
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DEPARTMENT OF THE INTERIOR UNITED STATES GEOLOGICAL SURVEY GEORGE OTIS SMITH, DIRECTOR BULLETIN 450 MINERAL RESOURCES OF THE LLANO-BURNET REGION, TEXAS WITH AN ACCOUNT OF THE PRE-CAMBRIAN GEOLOGY BY SIDNEY PAIGE WASHINGTON GOVERNMENT PRINTING OFFICE 1911 CONTENTS. * ' Page. Introduction.............................................................. 7 Topography............................................................... 8 Drainage................................................................... 8 Geology.......................................................:................ 9 General features........................................................ 9 Algonkian (?) rocks....................................................: 9 Geologic units...................................................... 9 Granites............................................................ '10 Geologic relations...............".............................. 10 Types and distribution........................................ 11 Petrography..................'..................-.-.---------- 31 Coarse-grained type........................................ 11 Medium to fine-grained types including some coarse varieties.. 12 Opaline quartz-feldspar porphyry type....................... 14 Schists and gneisses (Llano series).................................. 14 Divisions and distribution..................................... 14 Paeksaddle schist............................................... 15 Distribution and general character.......................... 15 Petrography.............................................. 17 Valley Spring gneiss............................................ 19 Distribution and general character.......................... 19 Petrography............:................................. 20 Origin of the schists and gneisses................................ 20 Basic intrusive rocks of a gabbro-diorite type......................... 21 General character and distribution................................ 21 Petrography.................................................. 22 Paleozoic rocks......................................................... 23 Upper Cambrian rocks.........:.................................... 23. Cambro-Ordoviciaii rocks............................................ 24 Carboniferous rocks................................................ 24 Structure.............................................................. 25 Iron ores................................................................... 26 General description, by A. C. Spencer.................................. 26 Special localities...................................................... 28 Olive property..................................................... 28 Bader tract........................................................ 31 Iron Mountain..................................................... 34 Keyser-Jones tract.................................................. 40 1 Goodwill prospect................................................. 41 Parkhill prospect.................................................. 42 Iron deposits near CastelU............................... J......... 42 Deep Creek ores............................\ .................. 42 'Elm Creek ores................................................. 45 Lively tract........................................................ 48 Section 13 and vicinity.............................................. 49 Riley Mountain..................................................... 54 3 4 CONTENTS. Iron ores Continued. Page. Origin of the iron ores. .........................................*......... 56 Possible hypotheses................................................. 56 General distribution of iron throughout geologic formations and the character of the accompanying beds. ........................... j. 56 Geologic relations of the iron ores...................................... 57 Characteristics of the ores........................................... 58 Bearing of igneous rocks of the region 6n origin of iron ore............ 60 Chemical relations........................................!........,.. 62 'Probable conditions at time of intrusion.... 1......................... 65 Comparison with other regions....................................... 68 Summary.......................................................... 69 Gold...........................................:......................... 70 Copper.................................................................... 73 Lead..................................................................... 75- Graphite.......................... -o ...................................:.. 77 Manganese............................................................... 82 .Rare-earth metals.......................................................... 83 General description of the deposit....................................... 83 The rare-earth minerals......:......................................... 85 Economic value ......'....................................... ......... 88 Zinc blende with fluorite gangue............................................ 89 Serpentine and talc........................................................ 90 Oil....................................................................... 93 Structural materials........................................................ 94 Marble............................................................... 94 Sandstone............................................................ 94 Limestone............................................................. 95 Granite............................................................... 95 Index..................................................................... 101 ILLUSTRATIONS. Page. PLATE I. Geologic map of Texas............................................ 7 II. General geologic and economic map showing locations of Burnet and Llano quadrangles, Texas...................................... 8 III. Economic and geologic map of I/lano quadrangle, Texas........ In pocket IV. A, Assimilation of schist fragment along borders at contact with granite; B, Banding of magnetite ore....................i....... 10 V. A, Folding of Upper Cambrian sandstone on Beaver Creek, near lead prospect; B, Pegmatite and granite intruding schist.............. 76 FIGURE 1. Local flowage of schist at granite contact.......................... 10 2. Cross section and plan of Olive mine............................ 30 3. Distribution of float and outcrops on Bader tract and vicinity..... 32 4. Surface crop and underground workings at Iron Mountain prospect. 35 5. Vertical section of ore body at Iron Mountain prospect............ 36 6. Ideal section showing relation of faulting to folding and erosion... 37 7. Stereogram illustrating condition which would exist if the north fault passed vertically but at an angle to the strike of the fold.. 38 8. Magnetite prospects on Keyser-Jones tract, southwest of Castell... 40 9. Distribution of magnetite near Deep Creek...................... 43 10. Distribution of magnetite near Elm Creek, northeast of Castell.... 45 11. Distribution of magnetite showings in northern part of Schneider's pasture .................................................... 47 12. Distribution of magnetite 2 miles east of Castell................. 49 13. Magnetite prospects in H. & G. N. Section 13................... 50 14. Relation of ore layers in pit south of Willow Creek in section 13.. 51 15. Sketch of 8-foot ore surface in magnetite gneiss.................. 52 16. Map showing location of pyrite deposits north of Click post-office and their relations to faxilts.................................... 54 17. Concentration of magnetite along edges of schist f ragment at grani te contact.................................................. ^... 61 18. Remnant of schist fragment in granite mass..................... 62 19. Prospect pits and shafts at Heath gold prospect................... 72 20. Map showing location of lead prospects north of Bluff ton and area covered by figure 21......................................... 75 21. Plan and ideal section showing relations of Upper Cambrian to underlying pre-Cambrian granite at lead prospects north of Bluffton..................................................... 76 22. Plan of workings at graphite property near Lone Grove.......... 79 5 U. 8. GEOLOGICAL SURV&Y BULLETIN 450 PLATE I Pennsylvanian Undifferentiated Silurian Cambrian and Undifferentiated Tertiary and Carboniferous Ordovician Algonkian<?> later effusives GEOLOGIC MAP OF TEXAS. See page 7. MINERAL RESOURCES OF THE LLANO-BURNET REGION, TEXAS, WITH AN ACCOUNT OF THE PRE-CAMBRIAN GEOLOGY. ____ By SIDNEY PAIGE. INTRODUCTION. The field work on which the following report is based was begun in the summer of 1908 under the direction of A. C. Spencer, who was assisted by the writer, and was completed in the fall of 1909 under the direction of the writer, who was assisted by Fred H. Kay. A. C. Spencer and W. S. Bayley cooperated in-the field work, and Mr. Spencer has contributed descriptions of certain of the iron-ore de posits. Howland Bancroft also spent a short time in the field. A general report on the Llano and Burnet quadrangles, to be pub lished in folio form, is now in preparation.® The present report deals chiefly with the geologic .relations of the pre-Cambrian rocks and the associated iron ores. The stratigraphic and structural relations of the Paleozoic and Cretaceous rocks are only briefly treated, but will be discussed more fully in .the later