. ~‘-w—__.. -I PETROLOGY AND PETROFABRKS ATTHE NEWTON FALLS PIT, STAR LAKE, NEW YORK Thesis for We Degree of M. S. MICHIGAN STATE UNEVERSITY James W. Villar 1956 -PETROLOGY AND PETROFABRIOS AT THE NEWTON FALLS PIT, STAR LAKE, NEW YORK By JAMES w. YLLLAR A THESIS Submitted to the School of Science and Arts of Michigan State University of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Geology 1956 If 3 ABSTRACT The Newton Falls Pit constitutes the northern portion of the Benson mines, located in the Precambrian complex of the Adirondack highlands. The results of field observations supplemented by the analyses of twenty-one oriented thin sections are presented with brief interpretations relative to the ancestry of the rocks comprising the area. The study revealed three major rock units: (1) "hanging-wall gneiss," (Z) pegmatites, and (3) "host rock." ”Host rock” is be- lieved to represent the oldest unit, and is interpreted as a portion of the ancient Grenville complex. The present rock has evolved in conjunction with extensive injection and soaking of the stratified rocks by magmatic fluids, emanations, and solutions. Petrographic and field evidences favor a magmatic origin for the "hanging-wall gneiss." The presence of exsolution perthites, plagioclase exhibiting complex twin patterns, and the proximity of textural and structural character- istics to rocks forming from the consolidation of a magma, causes considerable ambiguity in relating this unit to Grenville metasedi- ments. Pegmatitic intrustions represent the youngest rocks in the ii area; their injection took place after the "hanging—wall gneiss" was at least partially solidified. All the rock types have been subjected to intense deformation and metamorphism. The major structure consists of the eastern limb of a syncline, slightly overturned to the west, and plunging north. Numerous crenulations, almost entirely isoclinical and over- turned, are superimposed on the major structure. Parallelism of lineations, foliation, banding, and rock contacts are the general rule. Discordant relationships were observed when considering certain 10- calities in detail. Mapping of over 1,980 joint planes revealed an abundance of typical ac and bc tension joints, but generally the pattern is haphaz- ard. Orientation analyses of the c-axes of nearly 3,000 quartz grains indicated only weak point maxima near a. For the most part, quartz orientations appear independent of major structural features. A petrofabric study of biotite revealed a strong concentration of flakes parallel to the inferred ab plane. Nearly complete obliteration of all cataclastic and relix tex- tures resulted from postdeformational intrusions of emanations and solutions. Extensive recrystallization has further masked pre-existing textures. iii The emplacement of iron ore is believed postdeformational. Iron oxides replace all minerals, but indicate a preference for ferro- magnesium minerals, especially biotite. The nonmagnetic ore is believed to be martite, which in part occurs at the grain boundaries of magnetite, appearing as an oxidation product. iv ACKNOWLEDGMENTS The author wishes to express his most sincere thanks to Dr. J. W. Trow for his direction and aid in completing this study; also to Dr. J. Zinn, Dr. B. T. Sandefur, and Dr. H. B. Stonehouse for their helpful suggestions and constructive criticisms. He is also greatly indebted to Dr. R. M. Crump and Mr. F. J. West of the Jones and Laughlin Steel Corporation for their COOpera— tion and direct assistance in providing much of the information cited. TABLE OF CONTENTS INTRODUCTION ............................... Location and Accessibility ...................... Physical Features and Climate .................. History and Production ........................ Regional Geologic Setting, ...................... Purpose and Scope ........................... PETROGRAPHY AND PETROLOGY ................. "Hanging-Wall Gneiss” ........................ Sample No. 9 ............................. SampleNo. 19 .................... Petrologic interpretations .................... Pegmatites ................................ Sample No. 5 ............................ _ . SampleNo.25 ......... Petrologic interpretations .................... "Host Rock” ............................... Sample No. 17 ............................ Sample No. 24 ............................ vi 13 14 18 19 22 23 29 31 33 Sample No. 12 ............................ Sample No. 35 ............................ Sample No. 22 ............................ Petrologic interpretations .................... STRUCTURAL GEOLOGY ........................ Structural Framework ......................... Minor Folds OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO Banding, Lineation, and Foliation ................. Joints and Faults ............................ PETROFABRIC S ............................... Quartz Orientation ........................... Biotite Orientation ........................... CON C LUSIONS SUGGESTIONS FOR FURTHER STUDY ............... RE FE RENC ES vii 39 41 46 46 46 47 48 52. 52. 59 64 67 69 TABLE II. III. IV. LIS T OF TABLES Modal Analyses of "Hanging- Wall Gneiss" ...... Modal Analyses of Pegmatites ............... Relation between Albite Rims on Grain Boundaries ............................ Modal Analyses of "Host Rock" .............. viii 28 32 Figure l. 10. 11. LIST OF FIGURES Index map showing location of problem area ...... Structure map showing foliation, joints, and locations of samples .......... . .......... Photomicrograph of sample 9 showing com- plex microperthitic intergrowth ............ Photomicrograph of sample 19 showing perthitic blebs uninfluenced by inclusions of quartz and magnetite ................. Photomicrograph of sample 5 showing the alteration of plagioclase to paragonite ....... Photomicrograph of sample 5 showing microcline-perthite and extensive altera- tion of secondary albite to paragonite ........ Photomicrograph of sample 25 showing secondary albite rim ................... Photomicrograph of sample 25 showing microperthite containing both exsolution and replacement blebs of albite ............ Photomicrograph of sample 24 showing untwinned potash feldSpar and replacing magnetite ........................... Photomicrograph of sample 24 showing frayed quartz grains, in crystallographic continuity, surrounded by chlorite .......... Same as Figure 10, using plain light ........ ix Page 12 12 21 21 24 24 34 34 35 Figure Page 12. Photomicrograph of sample 12 showing twinned microcline and fractures at grain boundaries ......................... 35 13. Photomicrograph of sample 35 showing subparallel orientation of large fresh biotite flakes ............................ 38 14. Photomicrograph of sample 35 showing large poikilitic garnet ...................... 38 15. Photomicrograph of sample 22 showing fractured quartz and fine aggregate of saussurite .............................. 40 16. Same as Figure 15, using plain light ........... 40 17. Eight hundred eighty poles to joints of ”hanging-wall gneiss" ..................... 49 18. One thousand one hundred poles to joints of “host rock" .......................... 49 19. Six hundred twenty-six quartz axes from sample 9 ............................... 54 20. Six hundred seventy-eight quartz axes from sample 19 .......................... 54 21. Four hundred thirty-six quartz axes from sample 5 ........................... 55 22. Four hundred forty-three quartz axes from sample 12 .......................... 55 23. Four hundred sixty- eight quartz axes from sample 35 .......................... 56 24. Four hundred seventy quartz axes from sample 22 .......................... 56 Figure 25. 26. 27. 28. 29. 30. Four hundred ninety-six poles to (001) cleavage in biotite from sample 9 .......... Four hundred ten poles to (001) cleavage in biotite from sample 19 ................ Two hundred sixty-four poles to (001) cleavage in biotite from sample 5 .......... One hundred seventy-one poles to (001) cleavage in biotite from sample 25 ......... Four hundred thirty-one poles to (001) cleavage in biotite from sample 35 ......... One hundred eighty-two poles to (001) cleavage in biotite from sample 22 ......... xi Page 60 61 61 62 62 INTRODUC TION Location and Ac c es sibility The Benson mines are located in the township of Clifton, St. Lawrence County, New York, approximately two miles east of Star Lake. The area investigated was restricted to the Newton Falls Pit extending from the property line to the northernmost stripping limit (Fig. 1). The Carthage and Adirondack branch of the New York Central Ra. ilroad provides freight and express accommodations extending from Carthage to Benson. Mines. Route No. 3, a main highway extending east and west across most of northern New York, passes the imme- diate vicinity of the mines. Physical Features and Climate The principal industries of the region are lumbering, paper manufacturing, mining, and agriculture. The terrain consists of low rounded hills with altitudes rang- ing from 900 to 1900 feet. The many small lakes and streams gen- erally drain to the north and northwest. With the exception of the stripped area at the Benson Mines most of the bedrock is covered 1 l I ' BENSON ME PIT AREA 35 d 1 JONES a W . g m m ,. .... \ . \ m i "" ‘ mun “WW I I_1_ s PIT—A I so IIIIIII // I p--’- “GI-INDEX MAP SWING LOCATION G’PROBIMAREA by a veneer of Pleistocene glacial deposits. The region is thickly wooded with pine, spruce, birch, maple, and poplar trees, and where the original timber has been cut there is extensive underbrush and second growth. Winters are severe, with heavy snowfall and recorded temper- atures as low as -45° F. Summers are mild, but there is consider- able rainfall during early Spring and late fall. History and Production Systematic mining was started in 1889, although ore bodies were mentioned in reports earlier than 1850 (Newland, 1908). Op- erations were intermittent until 1919, at which time, due to a com- bination of increased: production costs and decreased demands for iron ore, mining was discontinued. During July, 1941, new open-cut operations were resumed when the Jones and Laughlin Steel Corpora- tion leased the mine and adjacent prOperties (Millar, 1945). By add- ing new surface plants and employing more recent technological ad- vances, the capacity of the mines was greatly increased. More recent utilization of Humphrey's Spirals providing'gravity concentration of the extensive body of nonmagnetic ore has increased the output of con- centrates. Annual production at the present time is approximately 1,000,000 tons of magnetite concentrates and 600,000 tons of 1 nonmagnetic concentrates, all of which are sintered at the mines and shipped by rail to blast furnaces at Pittsburgh, Aliquippa, and Cleveland (West, personal communication). Regional Geologic Setting The most thorough studies of the Precambrian complex in the northwest adirondacks have been presented by Buddington (1939, 1948, 1952), Leonard (1951), and Engel and Engel (1953). It is gen- erally agreed by these authors that approximately 85 percent of the bedrock within the Highlands belt is igneous and 15 percent meta- sediments and migmatites of the Grenville series. The metasediments of the Grenville series are the oldest rocks in the region. In the Highlands belt these extremely variable metasediments have been intruded, incorporated, and to an uncertain extent granitized by later igneous magmas. In very general terms the dominant rock types comprise amphibolites of questionable origin, garnetiferous and sillimanitic paragneisses, quartzites, and marbles. Buddington (1948) has prOposed two major periods of domi- nantly granitic intrustion. The oldest of these is a quartz syenitic lThe nonmagnetic ore is locally termed "martite." Martite is defined by Dana (1951): "A name applied to Fe203 occurring in octahedral or dodecahedral crystals and pseudomorphous after mag- netite; perhaps in part also after pyrite." series ranging from pyroxene syenite to biotite granite along with minor pegmatitic development. Quartz syenite forms the major ele- ment of this complex. The entire series is thought to be due to consolidation of magma intruded from depth and variations in com- position effected by gravity stratification and incorporation of country rock. Following the intrusion of the quartz syenitic series the entire complex was subjected to orogenic forces that resulted in a series of intensely folded and deformed metasediments and intrusive sheets. Next followed the second major period of granitic intrustion which Buddington (1948) commonly refers to as the “younger granitic series." This series is predominately a hornblende granite with associated biotitic alaskite. Extreme differentiates include alaskite. microcline granite, and soda granite. Much of this granite forms conformable lenses and phacolithic masses in the older complex. The usual characteristic gneissic structure is thought by Buddington (1948) to have been inherited during a renewed period of deformation at the time of, and subsequent to, its emplacement. This brief summary of the major geologic events in the north- west Adirondack highlands is generally accepted as the most satis- factory hypothesis, with some minor modifications, by the majority of geologists who have studied the area. Purpose and Sc ope This thesis reports the results of a joint field and laboratory study of the Newton Falls Pit. Limited reconnaissance work was done during the summer of 1952. Field work was resumed during the summer of 1955, with detailed mapping of joint systems. The area was again visited in December, 1955, at which time the major- ity of samples were obtained. Petrographic and petrofabric exami- nations were made of twenty-one thin sections cut from nine samples. The purpose of the study was to provide preliminary data on the petrology and petrofabrics of the complex (deformed rocks) com- prising the area. PETROGRAPHY AND PETROLOGY Extraordinary mineralogical variations within relatively small localities seriously impede systematically subdividing the area into logical rock units. From the writer's field and petrographic obser— vations, only a general framework can be proposed, at best. The complex includes three general units, each possessing certain dis- tinctive characteristics relative to mode of origin, mineral assem- blage, Spacial relationships, and textures. These rock types are designated (1) ”hanging-wall gneiss," (2) pegmatites, and (3) "host rock"--names which conform with the terminology employed locally. "Hanging-Wall Gneiss" "Hanging-wall gneiss" borders the eastern portion of the Newton Falls Pit and extends beyond the area southward and eastward (Fig. 2). Locally the rock is sharply truncated a few hundred yards to the west by a generally north-south trending contact. Detailed study was restricted to the vicinity of samples 9 and 19 (Fig. 2), with only cursory field observations in other localities. The rock is fine- to medium—grained, and has generally a gneissic texture. In the vicinity of samples 9 and 19 the segregation into bands is not Mm4¢2