Precambrian oil inclusions in late veins of the White Pine copper deposit, Michigan

Excellent primary inclusions of petroleum were trapped in calcite crystals filling late veins which crosscut and offset the main copper ore zone at White Pine. The inclusions are now solid, but their spherical to hemispherical shapes indicate an original liquid state. Some inclusions were completely solidified by water-washing and/or bacterial degradation prior to enclosure by the calcite, whereas others (with one or more vapor bubbles) were still liquid at the moment of entrapment. P-T conditions of maturation and entrapment of this oil are defined by Nishioka and others (see abstract, this volume). Some of the Cu-Fe sulfides in the veins are closely associated with these hydrocarbons, forming crusts on the oil droplets and, in some cases, appearing to have veined and replaced oil solidified prior to its enclosure by younger calcite. In some veins, clots and spheres of dead oil are embedded in native copper in a manner indicating that the oil is at least as old as the metal. The age of the inclusion-bearing vein calcite (1047 +/- 35 Ma; Ruiz et al., 1984) provides a minimum age for the oil, and confirms the long-standing assumption (based on more debatable evidence) that the White Pine petroleum is truly Precambrianmore » in age.« less