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, Illinois top-ten "Charming Small Towns". Galena is located at (42.418171, −90.431472) along the Galena River, which is one of many tributaries of the Mississippi River. According to the 2010 census, Galena has a total area of , of which (or 99.83%) is land and (or 0.17%) is water. Galena is located in the Driftless Zone, an area that was not covered by glaciers during the recent ice ages. This area, which includes the far northwestern corner of Illinois, escaped glaciation, while almost the entire state was glaciated, nearly to its southern tip. Because it escaped glaciation, this area is known for