Geology and magnetite deposits of the Franklin quadrangle and part of the Hamburg quadrangle, New Jersey

Abstract

__________________________________________ Introduction and acknowledgments.__________________ Geography. ________________________________________ Previous work._____________________________________ Rocks of metasedimentary origin _____________________ Marble or metalimestone________________________ Quartz-potassium feldspar and associated gneiss____ Pyroxenic gneiss._______________________________ Garnetiferoxis gneiss and amphibolite____________ Hypersthene-quartz-oligoclase gneiss______________ Biotite-quartz-feldspar and associated gneiss_-__-Epidote-scapolite-quartz gneiss and associated rocks. Miscellaneous gneiss.___________________________ Stratigraphy of metasedimentary gneiss.______________ Orthogneiss._______________________________________ Metagabbro gneiss._____________________________ Syenite gneiss._________________________________ Igneous rocks._____________________________________ Pyroxene syenite, pyroxene granite, and pyroxene alaskite series._______________________________ Petrology.._-______-__________._____ Sparta Lake belt__________________________ Ford belt.__.-_- .-______.____.___________ Holland belt.______________________________ Hyper«thene granite, _______________________ Hornblende granite and alaskite__________________ Rocks of uncertain origin-___________________________ Amphibolite_ ___________________________________ Quartz-oligoclase gneiss._________________________ Biotite-quartz-oligoclase gneiss._______________,..._ Albite alaskite________________________________ Quartz-microcline gneiss.________________________ Dikes.____________________________________________ Petrogenesis ______________________________________ Pyroxenic gneiss._______________________________ Quartz-potassium feldspar gneiss and associated epidotic gneiss._______________________________ Quartz-oligoclase rocks._________________________ Hypersthene-quartz-oligoclase gneiss__________ Quartz-oligoclase gneiss (Losee Gneiss)________ Amphibolite_ _ ________________________________ Quartz-microcline gneiss.________________________ Hornblende and pyroxene syenite orthogneiss_____ Granitic and syenitic rocks_______________________ Metamorphic facies_____________________________ Franklin block.____________________________ Beaver Lake block__________________________ Ryker Lake block_________________________ Comparison with nearby areas._______________

Precambrian geology and magnetite deposits of the New Jersey highlands in Warren County, New Jersey

“…Drake (1969), however, pointed out that the NaO/KO ratios of most graywackes are too low to account for the high sodium content in the oligoclase-quartz gneiss. Baker and Buddington (1970) showed, on the basis of field studies, that the weight of evidence for either a magrnatic or a sedimentary origin for this unit is about the same. On a small scale, the oligoclase-quartz * gneiss has discordant contact relationships with the surrounding rocks, but on a large scale it is concordant.…”

“…Triangles are data from Baker and Buddington (1970?; squares are data from Drake (19o9)j closed circles are data from this study. Q, quartz; A, alkali feldspar including .albite up to Arui and P, plagioclase.…”

“…The classical hypothesis for the origin of these deposits is that the unique"and distinctive pyroxenite associated with the gneiss-enclosed deposits is a contact-metasomatic skarn developed by fluids emanating from alaskite intrusions and that the ores are, therefore, of pneumatolytic origin ^.ar they are spatially and genetically associated with these pyroxene-rich skarns. However, the occurrence of magnetite concentrations in sharply bounded tabular- 'f 9 shaped bodies, the absence of large igneous intrusions which could have been the source of residual iron- (Sims, 1958;Drake, 1969Drake, , 1970and Baker and Buddington, 1970). Recent hypotheses regarding the genesis of the magnetite deposits are diverse and include 1) introduction of iron by residual fluids from hornblende granite and alaskite to form contactmetasomatic skarn deposits (Sims, 1953(Sims, » 19585 2) release, transport, and concentration of iron through recrystallization-and deformation of amphibolite during regional metamorphism (Hagner and Collins, 1955;Collins, I969a, 1969b); and syngenetic concentration of iron by sedimentary processes prior to metamorphism (Baker and Buddington, 1970).…”

“…However, the occurrence of magnetite concentrations in sharply bounded tabular- 'f 9 shaped bodies, the absence of large igneous intrusions which could have been the source of residual iron- (Sims, 1958;Drake, 1969Drake, , 1970and Baker and Buddington, 1970). Recent hypotheses regarding the genesis of the magnetite deposits are diverse and include 1) introduction of iron by residual fluids from hornblende granite and alaskite to form contactmetasomatic skarn deposits (Sims, 1953(Sims, » 19585 2) release, transport, and concentration of iron through recrystallization-and deformation of amphibolite during regional metamorphism (Hagner and Collins, 1955;Collins, I969a, 1969b); and syngenetic concentration of iron by sedimentary processes prior to metamorphism (Baker and Buddington, 1970). (Bayley, 1910, 19^1;Bayley et al, 191^)i and very little detailed mapping has been done in the area of this study.…”

“…Plot of amphibolite modes. End members are quartz, Q; sum of mafic minerals, M; and plagioclase, P. Triangles are data from Baker and Buddington (1970)? squares are data from Drake (1969)?…”