They include massive sulfides, breccia sulfides, a breccia containing mineralized schist fragments in a sulfide matrix, stringer ore, and a low-grade siliceous ore. Although the predominant minerals are pyrrhotite, chalcopyrite, pyrite, and cubanite, accessory minerals such as niccolite, maucherite, galena, sperrylite, hessite, and several minerals of the platinum group are present. The floor, or footwall, rocks are generally Archean granites and Proterozoic volcanic and sedimentary. The Sudbury breccias are so called because of a singular absence of lithologic mixing. The matrix and the fragments are typically composed only of the rock type in which the breccia occurs.
Shatter cones are structures that crosscut lithologic contacts.
All three of these features have been widely attributed to shock metamorphism resulting from meteorite impact, although pseudotachylite brecciation and shatter cones can both be caused by tectonic stresses. The foregoing section has presented evidence that has been applied differently by different investigators. There is some doubt that a meteorite slammed into the Precambrian surface at all. Some have pointed out that it is fortuitous in the extreme that a meteor happened to hit not only at the junction of four tectonic provinces, but also in a single area within thousands of square kilometers where volcanic activity was already established. Others suggest that Lake Wanapitei, a younger subcircular lake basin at the northeast end of the Sudbury basin, was the point of impact that formed the shatter cones and some of the breccias.