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Geology of Dover Magnetite District Morris Co NJ Geological Survey 982-G 1953
Geology of the Dover Magnetite District Morris County New Jersey Geological Survey Bulletin 982-G by Paul K Sims
Soft Cover
Pages 245-310 + 5 maps(plates) #24-26 (LARGE Foldout maps)
Copyright 1953
CONTENTS
Abstract 245
Introduction 247
Geography 248
Rock units 250
Metasedimentary rocks 251
Calcareous rocks 251
Marble 251
Serpentine 251
Pyroxene gneiss 252
Skarn 252
Amphibolite 253
Origin of calcareous rocks 253
Quartzose rocks 255
Biotite-quartz-feldspar gneiss 255
Oligoclase-quartz-biotite gneiss 255
Origin of quartzose rocks 257
Undivided metasedimentary rocks 257
Mixed rocks 258
Igneous rocks (pre-Cambrian) 258
Quartz diorite and related facies 258
Albite-oligoclase granite 259
Hornblende granite and related facies 259
Hornblende granite 259
Microcline granite gneiss 259
Alaskite 260
Microantiperthite granite 260
Biotite granite 260
Granite pegmatite 260
Origin of the pre-Cambrian igneous rocks 261
Diabase (Triassic ?) 263
Structure 263
Folds 263
Structure of the metasedimentary rocks 264
Structure of the igneous rocks 265
Foliation 267
Lineation 267
Fracture cleavage 268
Faults 268
Joints 269
Magnetite deposits 269
General character 269
Distribution 272
Structure of deposits 273
Microbrecciation 277
Mineralogy 277
Opaque minerals 277
Magnetite 277
Hematite 278
Ilmenite 278
Pyrrhotite 278
Chalcopyrite278
Pyrite 278
Nonopaque minerals 279
Apatite 279
Spinel 279
Quartz 279
Calcite 279
Biotite 280
Pumpellyite 280
Chlorite280
Serpentine 280
Tourmaline 280
Sphene 280
Chemical composition 281
Origin and classification 282
History and production 287
Extraction and beneficiation of ore 288
Future of district 289
Principal mines and prospects 290
Mount Hope mine 291
Richard mine 295
Scrub Oaks mine 298
Hibernia mine 300
Hibernia Pond anomaly 301
References cited 302
Index 305
ILLUSTRATIONS
PLATE 24. Geologic map and sections of the Dover magnetite district, Morris County, N. J In pocket
25. Isometric block diagram of part of Mount Hope mine In pocket
26. Map and sections of Hibernia mine In pocket
27. Plans and sections of the Taylor ore body, 1,700 and 1,900 levels, Mount Hope mine In pocket
28. Plan of no. 6 level, Scrub Oaks mine In pocket
FIGURE 58. Index map showing the location of the Dover district, Morris County, N. J 249
59. Alaskite with conformable layers, streaks, and wisps of meta-sedimentary rocks 266
60. Lineation in biotite-quartz-feldspar gneiss 267
61. Polished specimen of gneiss ore from the Mount Hope mine 270
62. Polished specimen of low-grade skarn ore from Taylor ore body, Mount Hope mine 271
63. Block diagram showing idealized structure of ore bodies in the Dover district 274
64. Photomicrograph of sub-ore from dump at Brotherton mine 283
65. Polished specimen from Mount Hope mine showing magnetite in granite pegmatite 286
INTRODUCTION
The Dover district has been an important source of iron ore for over. 100 years, and has been active since about 1710. The total production from the district is estimated to be about 26 million tons of iron ore valued at about $100,000,000. This is approximately 70 percent of the total iron ore production from New Jersey. The district now produces about 500,000 long tons of iron ore annually from three mines-the Scrub Oaks, Richard, and Mount Hope. This is about 10 percent of the total annual iron ore production from the Northeastern States.
Inasmuch as a comprehensive geologic survey of the Dover district had never been made, a detailed study was begun in 1947 by the U. S. Geological Survey, in cooperation with the New Jersey Bureau of Mineral Research at Rutgers University. The work was carried out by the writer under the general supervision of A. F. Buddington.
This report contains a brief description of the geology, magnetite deposits, and principal mines. A comprehensive report that will record detailed descriptions of all mines, geologic maps of accessible mine workings, and a more interpretative discussion of the geology is in preparation for publication as a Professional Paper by the U. S. Geological Survey.
The more important geologic studies that have been made in the region are those of Rogers (1836, 1840) , Kitchell (1856) , Cook (1868) , Putnam (1886), Nason (1889), Wolff (1894), Bayley (1908, 1910, 1914) , Spencer (1908) , and Smith (1933) . These reports deal primarily with the broader features of the geology or with descriptions of individual mines; none are comprehensive in their scope. Many able geologists of the New Jersey State Geological Survey have studied the New Jersey iron deposits during the past century, and the principal report on these studies (Cook, 1868) contains much information on individual mining properties together with a summary of the geology known at that time. During the first decade of this century, Bayley surveyed the region that includes the Dover district and the results are recorded in three principal publications (Bayley, 1908, 1910, 1914). His investigations were carried out when mining in New Jersey was more widespread than at present and he was able to examine some mines that are now completely inaccessible, or even destroyed. The report on the iron mines of New Jersey (Bayley, 1910) is now the most complete source of data on the history and production of the mines in the district, but it gives only a brief summary of the geology.
The present investigation was made during 1947, 1948, and 1949, and 14 months were spent in the field, surveying the surface and underground geology. The district was mapped on 7l/2-minute topographic maps prepared by Army Map Service (scale: 1-25,000). Where greater accuracy was desired the geology was plotted on contact prints of aerial photographs having a scale of approximately 1,700 feet to 1 inch, and later was transferred to the topographic maps. About 25,000 feet of underground mine workings were mapped in the Scrub Oaks, Richard, and Mount Hope mines on scales of 30 or 50 feet to 1 inch. A plane table geologic map (scale 200 feet to 1 inch) was prepared at Mount Hope mine.
To support the field investigation about 650 thin sections and 25 polished sections of ore were studied.
During the field work the writer was ably assisted by several members of the U. S. Geological Survey. P. E. Hotz spent 2 weeks in the field with the writer during June 1947. E. S. Davidson assisted for 9 weeks during 1947 and for 16 weeks during 1948; G. S. Koch assisted for 16 weeks during 1949; and L. Pavlides assisted for 6 weeks during 1948.
The mining companies in the district cooperated fully in every way possible.
The laboratory studies were carried out in the geology department at Princeton University. The chemical analyses and some of the thin sections were furnished by Princeton University.
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