58 NEW YORK STATE MUSEUM 



The most interesting and important magnetite deposits occur in 

 the village of Port Leyden and on the west side of the river below 

 the bridge. Many years ago several attempts were made to mine 

 the ore here. An ore pit, now filled with water, was run down 

 some 50 or 60 feet and a furnace was erected, but the mine was 

 never a paying proposition. Ore was later brought to the furnace 

 from other places. The ore is magnetite associated with much iron 

 pyrites and often with quartz. A thin section of the ore from the 

 pit shows c^ofc of quartz; 45;^ of magnetite and pyrite and 5^ of 

 badly decomposed ferro-magnesian minerals. The wall rock from 

 the pit shows 35^ of feldspar, chiefly microperthite and some oli- 

 gogclase ; 45^ of quartz and 2ofc of biotite, pyrite, sillimanite, zircon 

 and garnet. Thirty feet from the ore pit, the feldspar content is 

 somewhat higher and the dark minerals not so prominent. Still 

 farther away the rock is much like a quartzose syenite. A few rods 

 from this pit and at the water's edge, an irregular shaped ore body 

 several feet across may be seen. It is nearly pure magnetite and 

 entirely surrounded by syenite. The ore is in no sense sharply 

 separated from the country rock. A rapid but perfect gradation 

 of the ore into the syenite may be seen and the evidence seems con- 

 clusive that this small ore body, at least, is a segregation mass in 

 the syenite. The ore in the pit is thought to have a similar origin, 

 although the evidence is not there quite so conclusive. This ore is 

 closely associated with syenite and garnetiferous gneisses in a 

 syenite-Grenville area and it is interesting to note that the Salis- 

 bury Iron Mine described by Gushing on the Little Falls quad- 

 rangle, and the occurrences noted by the writer on the Remsen 

 quadrangle, all show similar relationships to the country rock. It 

 would seem that when the molten syenite was passing through the 

 Grenville the conditions were somehow made favorable for the 

 segregation of the magnetite. 



Lead ore 



Before the middle of the last century lead ore was, discovered in 

 the Trenton limestone about a mile a little west of north of 

 Martinsburg. The early attempts to mine the ore and extract the 

 metal failed because of the small quantity of ore available. Th-j 

 ore is galena (sulphid of lead) which occurs in true vein deposits 

 and associated with calcite as a gangue material. The calcite is 

 frequently crystallized in six-sided prisms capped by three-sided 

 pyramids. The vein-stuf¥ fills joints in the limestone and the galena 

 has doubtless been dissolved out of the surrounding rock and de- 

 posited "in the veins. 



