Ore genesis accumulation of hematite gravels called "pisolites" which form channel-iron deposits. These are preferred because they are cheap to mine. Lead-zinc deposits are generally accompanied by silver, hosted within the lead sulfide mineral galena or within the zinc sulfide mineral sphalerite. Lead and zinc deposits are formed by discharge of deep sedimentary brine onto the sea floor (termed "sedimentary exhalative" or SEDEX), or by replacement of limestone, in skarn deposits, some associated with submarine volcanoes (called volcanogenic massive sulfide ore deposits or VMS), or in the aureole of subvolcanic intrusions of granite. The vast majority of SEDEX lead and zinc deposits
Galena Historic District Places. The Galena Historic District contains more than 1,000 buildings constructed before 1900 that are considered contributing properties. The center of downtown Galena is laid out in three parallel segmental tiers starting at Main Street closest to the river. Beyond Main Street, and at a higher elevation, are Bench and Prospect Streets. Main Street forms the primary commercial strip through Galena and is lined with buildings two, three, and four stories tall. Most of Main Street's structures are built of red brick and cast in Federal style of the simple commercial style of the 1840s. On Bench Street, most of