VIRTUAL FIELD TRIP TO THE KEWEENAW PENINSULA, MICHIGAN -  ORE FORMATION II     

Copper has totally filled the vesicles in the top of a basalt flow. Seaman museum specimen	Specimen from the top of a basalt flow showing amygdaloids filled with calcite (white) and adularia (red). Wolverine #4, specimen is 5 cm. across.

Copper is almost exclusively in amygdaloids. 10 cm across. Following four photos are Knowton amygdaloid, Caledonia Mine.	Primarily copper in amygdaloids, but significant replacement of copper around the voids. 3 cm across.

    

Some copper occurs in vesicles, but a significant amount occurs in breccia. 3 cm. across	Almost all of the copper occurs in the breccia. 2 cm across.

           

Calcite and epidote vein filling in brecciated basalt flow top. National mine, specimen is 15 cm. across.

 

This is a picture of a vertical vein near the portal of the Nebraska mine. Although the copper tends to fill in open spaces in the volcanic beds, there were fissure veins that cut across these beds. This section shows the alteration mineralogy that occurred near the hydrothermal veins. (Field of view is 2m across)	Although there was little time between when the Pleistocene glaciers exposed new areas of mineralization to the action of weathering, there has been some minor development of secondary copper minerals such as malachite. Most of this material is relatively massive crusts and is only poorly developed on the surfaces (Nebraska portal area 20cm. across)

 

40 cm boulder on Allouez No. 3 dump. Note the color variation of the alteration along the vein (calcite is in the center, a bleached zone surrounds the vein symmetrically, a thin hematite rich band, unaltered basalt.

 

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