UNITED STATES DEPARTMENT OF THE INTERIOR Harold L. Ickes, Secretary GEOLOGICAL SURVEY W. C. Mcndenhall, Director Bulletin 920 PRE-CAMBRIAN GEOLOGY AND MINERAL RESOURCES OF THE DELAWARE WATER GAP AND EASTON QUADRANGLES, NEW JERSEY AND PENNSYLVANIA BY W. S. BAYLEY UNITED STATES GOVERNMENT PRINTING OFFICE WASHINGTON : 1941 For gale by the Superintendent of Documents, Washington, D. C. ....... Price 40 cents CONTENTS Page Abstract__ ____-__--________________-__-----_-_____-_____-..._-__ 1 Introduction._----___-_-_-___-___-______._-_-___---_-_-____-______ 3 Topography. _ ______________________________________ ____________.._ & General geology.------_--__-_-__-_--_-_-_---___-___________-______ 7 Highland belt......._.. .............._ .._................. 8- General features..._---_--_--____-____-_-_-_.._-_____-._____ 8' Franklin limestone--.--------.-___-_-_-_______-_____-___.__ 9' General character and occurrence._..-_----_--__._---_-_- 9' Composition __.__. ____________________________________ 10 Distribution___________________________________________ . 11 Pickering gneiss_----_-__-_--_-_-^-_------__-_____-___-_-__ 12 Distribution _____-_-_-_-_--__-_-__--_-________________ 12 Varieties.____________________________________________ 13 Principal areas of Franklin limestone and Pickering gneiss._____ 19 General distribution_____--_-___-_-_-_-_-___________-__ 19 Lower Harmony and Roxburg areas_____________________ 20 Pequest area._________________________________________ 22 Chestnut Hill area_-----_------_-_---______-._-_____- 26 Structure of Franklin limestone and Pickering gneiss____--_-__- 42 Relations of Franklin limestone and Pickering gneiss to sur­ rounding rocks.____-__--_------_---_-____--_-___---____ 43 Age of Franklin limestone and Pickering gneiss._-._--._-_-_-._ 45 Intrusive gneisses...-______________________________________ 46 General features..___,-_--_--_-__----__-___-__--__----- 46 Pochuck gabbro gneiss.________________________________ 47 Losee diorite gneiss___-----------------_-_-_-_-__-__-_- 49 Byram granite gneiss__---__-----_----__-----_-.__------ 50 Chemical relations of the several gneisses.-____-_____--__- 51 Pegmatites.______________________________________________ 52 General character and distribution..._.___._-___-________ 52 Composition and age___--___--------------------_____-_ 52 Economic geology.__--_-_----__-_---_-___..__-__---___-__--___--_-- 53 Economic products___________------_-_--_-_-_-_______-___-____ 53 Magnetite.___________________________________________________ 54 Mine openings.___--_-___-_-___-_---_____________-__--____ 54 Occurrence of the ore.-___--_--------_-__--_-------___--_._ 55 Magnetiferous pegmatite.______________________________ 55 Ore bodies in the gneisses and schists.........---._..--_-_- 55 Ore veins.________________________________________ 55 Shapes of the ore bodies.___________________________ 56 Character and mineral composition of the ore.-------- 58 Ore bodies in the Franklin limestone._------------------- 59 Chemical composition of the ore___--_-_--_--__-----__-----_- 59 Origin of the ore_______-_--________________--_-____--_-__ 60 Other views on the origin of the ore.___-_----.--------_.----- 63 in IV CONTENTS Economic geology Continued. Magnetite Continued. Page Comparison with the magnetic ores of the southern Appalachians. 66 Magnetite mines_.________________________________________ 66 Mines in the Franklin limestone. - _______________________ 67' Openings in the limestone____--________________ .___ 67 Ahles mine__--___-__ _-_-_---__--_______________ 68 Production of the mines in limestone.._______________ 69 Mines in the gneisses and schists._______________________ 69 Washington mine_____--_--__------___--___________ 70 Durham mine.__________-___________i___________^_ 71 Barton, Kaiser, -West End,<and Swayze mines... ___..____ 76 Titaniferous magnetite mines._.-__________.__.____..___ 76 Hematite.-_----_:--------------------.----------_---.-_-___._. 77 Mine openings_____-_----_-----_-._----_-_--______________ 77 Marble Mountain mine_____--__----_-_______-________ 77 Titman prospect___-.__-_--_---_---__--.______________ 78 Limonite. ____-__-----___--___-______-___--_____._--______-____ 79 Mine openings.___-__-__---__-_--------__-_____J_________- 79 Occurrence of the ore.___--_-____--__--___________.________ 81 'Chemical composition..____________________________________ 81 'Origin..... __________________________________________ 82 Limonite mines-----__----_-_------___--__-_-__.___________ 85 Williams shaft.___-____-.---_-_-__-_-______-__________ 85 Shoemaker mme-_-------_-----__-_-_--____--_-___-____ 86 Orchard mine.__-_-_____--___-__- --_-_______-__-_--.__ 87 Other limonite mines_-_-__------_-----____--_-_________ 87 Pigments---..---------.--------- _________ _.--__._______ 88 Zinc--..------------------------------------_-_--___-____ 88 Kaolin. __-_.-_--------.------__________________________ 89 Marble and serpentine.__-__-_--___----_----_____-_____________ 90 Flux and portland-cement rpck______________________________ 91 Stone for building and interior decoration____________,________ 91 Mineral pulp__________-___'_---_-___--___-___--__________ 93 Stucco, terrazzo, and roof granules_________--__-_-_.-.___._ 93 Lime_ _ ____________________________________________________ 94 Talc.__-------------_-------------------------------_-------. 94 Asbestos- _ ____--.--_----__--_------------------__-------_-.-__ 95 Mica_ _________-___-___-------__------_------__--_---_-_.___ 95 Products of the Paleozoic formations..._-----_-_-______^_________ 95 Index.______-_..__-_-_-____-------------------------------------_ 97 ILLUSTRATIONS Page PLATE 1. A, Photomicrograph of gneiss, bank of Delaware River about 2 miles north of Easton, Pa.; B, Photomicrograph of quartz- sericite schist, Fulmer mine, west end of Marble Mountain. __ 12 2. Polished slab of gneiss, showing injection of dark schist by granitic material, Washington mine, near Oxford, N. J..__- 52 CONTENTS V Page PLATE 3. A, Photomicrograph of Losee gneiss near Mountainville, Tewkesbury County, N. J.; B, Photomicrograph of Byram gneiss, road half a mile north of Williams mine, Vernon Town­ ship, Sussex County, N. J_______---_-_____------______._ 53 4. Sections through the ore bodies of the Weldon mine__________ 60 5. Geologic map of the pre-Cambrian and Lower Cambrian (Hardy- ston) areas in the Delaware Water Gap and Easton quad­ rangles. ______-__-___--_-_--___---------_-----__---_ In pocket FIGURE 1. Index map of New Jersey and adjacent States.---.--------- 4 2. Sketch map showing areas of pre-Cambrian crystalline rocks in New Jersey and adjacent States--__---_--------__-___- 5 3. Diagrammatic plan and sections of ore shoots of magnetite in the gneisses and schists of the Highlands__---_-_________ 57 4. Map of surface at Ahles mine--_---_-_---_----------_--_-- 69 PRE-CAMBRIAN GEOLOGY AND MINERAL RE­ SOURCES OF THE DELAWARE WATER GAP AND EASTON QUADRANGLES, NEW JERSEY AND PENNSYLVANIA By W. S. BATLEY ABSTRACT The' area whose geology and economic products are described covers a belt 8 to 10 miles wide extending from Buttzville, N. J., south westward about 16 miles. Although the first field work by the Geological Survey was done in 1906, in anticipation of the publication of a folio of the geologic atlas on the area, supplementary studies were carried on in 1926, 1929, and 1931. In the 25-year interval there were many changes, but in view of the present renewed activity in the iron industry and the fact that this report locates and describes many old mines at which conditions are now obscured, the manuscript has been left essentially in its original form because it furnishes valuable information concerning old workings which it may be desired to reopen. Moreover, it affords an excellent record of scientific details of the local pre-Cambrian geology and of the ore deposits. Topography and a/real geology. The northern part of this area is crossed by a series of ridges representing a part of the Highland belt in New Jersey and Pennsylvania, and the southern part is intersected in a general southerly direction by the Delaware River. Pre-Cambrian rocks, mainly gneisses, com­ pose the ridges, between which are Paleozoic limestone and shale, which also form the wide valley bordering the ridges on the north. South of the ridges is the Piedmont Plateau, underlain by conglomerate, sandstone, and shale of the Newark group except in a few narrow strips at the bases of the ridges, where Paleozoic beds crop out. In this region there is shown more clearly than elsewhere in the Highlands the series of metamorphic rocks which are intruded by the predominant gneisses of the New Jersey Highlands. Pegmatites occur throughout the region in association with gneiss, limestone, and other rocks. Although commonly occurring in sheets parallel to the associated limestone and gneiss, some pegmatite dikes cut across the structure of these rocks, indicating that the pegmatites are younger. The principal min­ erals of the pegmatites are the same as those in the gneisses, that is, quartz, microcline, microperthite, oligoclase, hornblende, pyroxene, biotite, and in places magnetite, graphite, and muscovite. Hornblende is abundant in dikes that are associated with magnetite ores. In some of the pegmatite bodies the proportion of magnetite is so great that the rock has been mined as lean iron ore. Mineral resources. The principal economic products obtained from the pre- Cambrian rocks of this area are magnetic iron ore, marble used in the manu- 2 DELAWARE WATER