21. Iron - A Short Collecting Trip
Last Updated: 14th Feb 2016By Frank Festa
Post Date: April 16, 2014Trip Date: 2010 - 2014, On Going
Iron – A Short Collecting Trip
My son and I were on the trail of iron ore and living in the western side of Pennsylvania, which in years past, supposedly had deposits that were noted as being inexhaustible. The geology and history of Pennsylvania is far too diverse and intricate to properly discuss here but massive amounts of information has been written about both subjects. This article can only hit on some of the notable points
Before becoming a Commonwealth, Pennsylvania was home to Native American Indians, the Delaware, Susquehannock, Iroquois, Eriez, Shawnee, and other Nations.
On February 28, 1681, Charles II granted a land charter to William Penn to repay a debt he owed to William's father, Admiral William Penn. Admiral William Penn was one of the most famous of the old England’s naval heroes. In order to liquidate a debt of £16,000 due the Admiral for services and advances to his country and the English monarch, Charles II, granted to Penn's son the charter for 28,000,000 acres of land which constituted the State of Pennsylvania. This was one of the largest land grants to an individual in history. It was named Pennsylvania by the king himself. When Admiral Penn passed away his son become the heir of his estate. The king who spent all the money he could get, was not likely to pay back loans soon. In 1680 William Penn asked King Charles to grant him a tract of land in America as payment of this debt. The king, after some reflection, realized this was an easy way to get out of debt by giving away land that belonged to the Indians.
Pennsylvanian iron ores consist of several varieties; hematite (Fe2O3), magnetite (Fe3O4), limonite (Fe2O3.H2O) and siderite (FeCO3), bog ore which are deposits that develop in bogs or swamps by the chemical or biochemical oxidation of iron carried in solutions consist primarily of iron oxyhydroxides, commonly goethite (FeO(OH)). Also, small deposits of pyrite (FeS2) and ilmenite (FeO.TiO2), but these two are not suitable for iron extraction. Iron ore is defined as a mineral or group of minerals containing sufficient iron to be economically used in iron production. Iron ores were mined within the boundaries of Pennsylvania until production shifted to the Lake Superior region in the 1870’s.
In Pennsylvania magnetite was the principle ore mined along with brown ore (limonite). Iron ore in Pennsylvania is found in igneous, metamorphic and sedimentary rocks. In sedimentary rocks the ore is present as iron oxides (limonite, goethite, or hematite), iron carbonate (siderite), and iron silicates (chamosite, glauconite, and greenalite). The distribution of iron ore through pathways along thrust faults, cross-strikes, structural discontinuities, and permeable sandstone are theorized to have conducted warm reactive fluids rich in iron and silica. Where these fluids interacted with local carbonate rocks, iron precipitated as iron carbonate (siderite) which is commonly oxidized to limonite and other oxides. The deposits are known to exist from the central Appalachian Mountains and extend from the Blue Ridge Province of Pennsylvania to the western edge of the basin in Ohio.
Igneous and metamorphic rocks, located mainly in eastern Pennsylvania host magnetite and hematite ore. Hematite was mined at Durham, Bucks County, within metasedimentary rock. The magnetite generally is found in quartz-oligoclase gneiss, amphibolite, pyroxene gneiss, quartz-potassium feldspar gneiss and marble skarn. Magnetite also is found as a replacement of carbonate rocks in southeastern Pennsylvania. This ore is referred to as the Cornwall-type, named after the first known deposit in Cornwall, Pennsylvania where an estimated 153 million tons of magnetite ore was produced from the Cornwall Mine.
In Pennsylvania, the sedimentary rock layering host some very distinctive ores. The ores, which may be primary or secondary, include many compounds which are mainly oxides. The minerals generally associated with sedimentary iron deposits can include: limonite, siderite, magnetite, and hematite.
Iron may be incorporated into a sedimentary deposit at the time of deposition or may form later as a result of weathering or interaction with groundwater, a process known as secondary enrichment. Chemical sedimentation is the precipitation of an iron mineral out of iron-bearing water. Clastic sedimentation is the accumulation of iron mineral grains within the sediment. Weathering is the physical degradation of a sedimentary rock, and the following oxidation of an iron mineral. Solution–remobilization occurs when iron is chemically removed from adjacent lithologies and transported to another location and deposited.
Examples of iron deposits formed by chemical precipitation are the Clinton-type ore, the bog iron ore, the siderite ores and metallic sulfide deposits. Iron can be deposited within the cavities of sedimentary rocks by iron-bearing water. This precipitation of iron minerals such as iron sulfide (pyrite, marcasite), iron carbonate (siderite) or an iron oxide/hydroxide (hematite, limonite, goethite). Factors determining this process include temperature, pressure, oxidation state, pH, iron concentration, available sulfur and organic material. Precipitation of iron can occur prior to lithification of the sediments or at a later time during diagenesis. Additional iron minerals that may form during diagenesis are chamosite and glauconite. Also, exposure of sedimentary rocks to weathering can change the mineral form of the iron. For example, siderite beneath overburden changes to limonite at the outcrop.
Oolitic ferruginous strata known as Clinton ores are included among sedimentary iron deposits. The Clinton ore deposit is an extensive deposit which appears in the Appalachian region from New York to Alabama. The deposit is fossiliferous, fossilized structures being replaced by hematite. The Clinton Formation accumulated in shallow marine environment as Pennsylvania is known to have been at one time. It was been suggested that when ferrous iron is transported by various means, into a marine environment where solid calcium carbonate is in a balanced state with the sea water, iron will precipitate. The ferrous iron precipitates as ferric iron in the water and as a replacement of the calcium carbonate.
Iron can combine with sulfur to form iron sulfides. Biochemical processes influence the precipitation of sulfide deposits. Reducing or anaerobic environments where sulfur is available favor pyrite formation. The black shales of Pennsylvania have a high pyrite content due to a large organic content. The presence of organic material and anaerobic sulfate in the sediment allows the development of pyrite because of the creation of a reducing geochemical environment where a low oxidation potential is necessary for sulfide formation.
Bog iron deposits are found in northwestern Pennsylvania. Bog iron forms where groundwater carrying dissolved iron enters an oxygenated area and precipitates the iron as hydrous ferric oxide. Bog iron was heavily used for the production or iron in the colonial iron furnaces of northwestern and northeastern Pennsylvania. Bog iron deposits are found in northwestern Pennsylvania in bogs, marshes, meadows, etc. Bog ore is a soft, spongy deposit of limonite that forms as a precipitate from iron-bearing water. Bog ores can be found within the sedimentary rocks as the result of chemical precipitation. Bog ore style of precipitation occurs when the ground water carryies dissolved ferrous iron until the iron becomes oxidized normally at the top of the water table or as it emerges into a marsh. Oxidized iron precipitates and forms a kind of ferruginous cement around the grains of the sand, silt and clay to form a hard crust. Repeated fluctuations in the water table level add to the thickness of the iron crust. Bog ore is red in color, and has a tabular, pisolithic, nodular, laminated or irregular aggregate form.
In central Pennsylvania, deposition of limonite ore above the Gatesburg Formation was generated under anaerobic, acidic conditions and precipitated along the top of this formation. Also, iron can be put into solution, say for instance, in a swamp here decaying organic material creates reducing environment, a low pH (acidic) condition. As the swamp water naturally percolates downward, the iron is transported to the bedrock. Here at the soil / rock interface it comes into contact with an alkaline carbonate surface where the iron precipitates along joints to build up into massive, irregular limonite forms. If the iron-carrying groundwater enters a large cavity, cave, the iron can deposit on the surface of stalactites and become incorporated into the limestone as an iron carbonate mineral.
Siderite (iron carbonate) is an iron ore mineral that composes beds or nodules that form during precipitation or as an alteration of preexisting carbonate concretions. The factors influencing their formation of iron sulfide or iron carbonate precipitation include the action of bacteria, the amount of marine sulfate in the sediment and a source of carbon is needed. Iron carbonate nodules or concretions generally form in deltaic or brackish water.
Siderite has been found in bogs and marshes. It forms around fragments of wood of metal or may form where there is a deficiency of sulfate. Siderite precipitates in the interstices of sediment incorporating the silt/clay particles within the concretion
Blackband ore is a siderite layer adjacent to a bed of peat is. The blackband siderite deposits require a low-sulfate, anoxic water chemistry.
Meteoric water is water slightly acidic, containing humic acids and carbonic acid, the ph is usually as low as 4.0 – 5.0 and it is oxidized. Weathering occurs when meteoric water attacks the minerals within the bedrock. Meteoric water can oxidize, hydrate and carbonize rock-forming silicate minerals. The interaction of meteoric water and carbonate rocks leads to the dissolution of limestone and dolomite. Residual minerals are left behind that were incorporated in the carbonate rock at the time of deposition. During normal weathering conditions, exposure to meteoric water leads to the removal of alkalies and alkali earths, sodium, potassium, calcium, and magnesium from the residual soil developed on the bedrock.
We continued along the rail bed until at last a tall rock layered cliff was in front of us. Within the rock layering we see the famous limestone of Pennsylvania, a coal vein of several inches in height and finally what they were looking for, the iron ore layer. This particular deposit could be found up to a foot in thickness.……iron ore. With much excitement and enthusiasm we pull out a streak plate. Holding their breath, the test confirms the ore to be hematite. We gather a number of specimens and load our back packs. After exploring the area, photo taking and a short break we begin their return trip following the railroad tracks back.
About a mile into their return trip we come across a hiker also walking the tracks coming in our direction. Naturally we all stop and chat, talk about their recent find. The hiker not so intrigued states “So, you’ve dug up some iron, the hills are full of it, so what”? Me being not only being in love with rocks but also a history enthusiast, especially local history, was slightly shocked with the hiker’s response. I would like to tell you a story if you have the time, I said to the hiker. We sat in the shade and I began……
Native iron rarely if ever exists in a pure state on the surface of the earth. How do we know that? Elemental iron is highly reactive to oxygen and or water especially saltwater. But, there are a few exceptions, meteoritic iron contains a high percentage of iron and can be found in small amounts all over the planet. The Hoba Meteorite, a sixty ton specimen fell to Earth and remained intact eighty thousand years ago. Then there are the massive blocks of native iron and iron carbide, weighing up to 22 tons, found at Uivfaq, Disko Island, Western Greenland. The iron blocks are associated with tertiary basalts that erupted during rifting between Greenland and Baffin Island, early in the opening of the Davis Strait. The iron is an assemblage of iron and iron carbide (cohenite). These boulders were found by a Swedish expedition, led by A. E. Nordenskiold, in 1870. Recently a new iron boulder was found in August of 1985 in Stordal about 70 km from the first find.
Happy Hunting
Frank
Iron – A Short Collecting Trip
In Search of Iron Ore
My son and I were on the trail of iron ore and living in the western side of Pennsylvania, which in years past, supposedly had deposits that were noted as being inexhaustible. The geology and history of Pennsylvania is far too diverse and intricate to properly discuss here but massive amounts of information has been written about both subjects. This article can only hit on some of the notable points
Before becoming a Commonwealth, Pennsylvania was home to Native American Indians, the Delaware, Susquehannock, Iroquois, Eriez, Shawnee, and other Nations.
On February 28, 1681, Charles II granted a land charter to William Penn to repay a debt he owed to William's father, Admiral William Penn. Admiral William Penn was one of the most famous of the old England’s naval heroes. In order to liquidate a debt of £16,000 due the Admiral for services and advances to his country and the English monarch, Charles II, granted to Penn's son the charter for 28,000,000 acres of land which constituted the State of Pennsylvania. This was one of the largest land grants to an individual in history. It was named Pennsylvania by the king himself. When Admiral Penn passed away his son become the heir of his estate. The king who spent all the money he could get, was not likely to pay back loans soon. In 1680 William Penn asked King Charles to grant him a tract of land in America as payment of this debt. The king, after some reflection, realized this was an easy way to get out of debt by giving away land that belonged to the Indians.
65 Pounds of Hematite
Streak Plate Test
Long and Narrow Ore
Pennsylvanian iron ores consist of several varieties; hematite (Fe2O3), magnetite (Fe3O4), limonite (Fe2O3.H2O) and siderite (FeCO3), bog ore which are deposits that develop in bogs or swamps by the chemical or biochemical oxidation of iron carried in solutions consist primarily of iron oxyhydroxides, commonly goethite (FeO(OH)). Also, small deposits of pyrite (FeS2) and ilmenite (FeO.TiO2), but these two are not suitable for iron extraction. Iron ore is defined as a mineral or group of minerals containing sufficient iron to be economically used in iron production. Iron ores were mined within the boundaries of Pennsylvania until production shifted to the Lake Superior region in the 1870’s.
53 Pounds of Magnetite
Magnetite Close-Up
Magnet and Magnetite
Black Streak
In Pennsylvania magnetite was the principle ore mined along with brown ore (limonite). Iron ore in Pennsylvania is found in igneous, metamorphic and sedimentary rocks. In sedimentary rocks the ore is present as iron oxides (limonite, goethite, or hematite), iron carbonate (siderite), and iron silicates (chamosite, glauconite, and greenalite). The distribution of iron ore through pathways along thrust faults, cross-strikes, structural discontinuities, and permeable sandstone are theorized to have conducted warm reactive fluids rich in iron and silica. Where these fluids interacted with local carbonate rocks, iron precipitated as iron carbonate (siderite) which is commonly oxidized to limonite and other oxides. The deposits are known to exist from the central Appalachian Mountains and extend from the Blue Ridge Province of Pennsylvania to the western edge of the basin in Ohio.
Igneous and metamorphic rocks, located mainly in eastern Pennsylvania host magnetite and hematite ore. Hematite was mined at Durham, Bucks County, within metasedimentary rock. The magnetite generally is found in quartz-oligoclase gneiss, amphibolite, pyroxene gneiss, quartz-potassium feldspar gneiss and marble skarn. Magnetite also is found as a replacement of carbonate rocks in southeastern Pennsylvania. This ore is referred to as the Cornwall-type, named after the first known deposit in Cornwall, Pennsylvania where an estimated 153 million tons of magnetite ore was produced from the Cornwall Mine.
In Pennsylvania, the sedimentary rock layering host some very distinctive ores. The ores, which may be primary or secondary, include many compounds which are mainly oxides. The minerals generally associated with sedimentary iron deposits can include: limonite, siderite, magnetite, and hematite.
Pennsylvania Siderite
White Streak
Iron may be incorporated into a sedimentary deposit at the time of deposition or may form later as a result of weathering or interaction with groundwater, a process known as secondary enrichment. Chemical sedimentation is the precipitation of an iron mineral out of iron-bearing water. Clastic sedimentation is the accumulation of iron mineral grains within the sediment. Weathering is the physical degradation of a sedimentary rock, and the following oxidation of an iron mineral. Solution–remobilization occurs when iron is chemically removed from adjacent lithologies and transported to another location and deposited.
Examples of iron deposits formed by chemical precipitation are the Clinton-type ore, the bog iron ore, the siderite ores and metallic sulfide deposits. Iron can be deposited within the cavities of sedimentary rocks by iron-bearing water. This precipitation of iron minerals such as iron sulfide (pyrite, marcasite), iron carbonate (siderite) or an iron oxide/hydroxide (hematite, limonite, goethite). Factors determining this process include temperature, pressure, oxidation state, pH, iron concentration, available sulfur and organic material. Precipitation of iron can occur prior to lithification of the sediments or at a later time during diagenesis. Additional iron minerals that may form during diagenesis are chamosite and glauconite. Also, exposure of sedimentary rocks to weathering can change the mineral form of the iron. For example, siderite beneath overburden changes to limonite at the outcrop.
Siderite with Limonite
Oolitic ferruginous strata known as Clinton ores are included among sedimentary iron deposits. The Clinton ore deposit is an extensive deposit which appears in the Appalachian region from New York to Alabama. The deposit is fossiliferous, fossilized structures being replaced by hematite. The Clinton Formation accumulated in shallow marine environment as Pennsylvania is known to have been at one time. It was been suggested that when ferrous iron is transported by various means, into a marine environment where solid calcium carbonate is in a balanced state with the sea water, iron will precipitate. The ferrous iron precipitates as ferric iron in the water and as a replacement of the calcium carbonate.
Iron can combine with sulfur to form iron sulfides. Biochemical processes influence the precipitation of sulfide deposits. Reducing or anaerobic environments where sulfur is available favor pyrite formation. The black shales of Pennsylvania have a high pyrite content due to a large organic content. The presence of organic material and anaerobic sulfate in the sediment allows the development of pyrite because of the creation of a reducing geochemical environment where a low oxidation potential is necessary for sulfide formation.
Siderite with Vug
Siderite Crystals
Bog iron deposits are found in northwestern Pennsylvania. Bog iron forms where groundwater carrying dissolved iron enters an oxygenated area and precipitates the iron as hydrous ferric oxide. Bog iron was heavily used for the production or iron in the colonial iron furnaces of northwestern and northeastern Pennsylvania. Bog iron deposits are found in northwestern Pennsylvania in bogs, marshes, meadows, etc. Bog ore is a soft, spongy deposit of limonite that forms as a precipitate from iron-bearing water. Bog ores can be found within the sedimentary rocks as the result of chemical precipitation. Bog ore style of precipitation occurs when the ground water carryies dissolved ferrous iron until the iron becomes oxidized normally at the top of the water table or as it emerges into a marsh. Oxidized iron precipitates and forms a kind of ferruginous cement around the grains of the sand, silt and clay to form a hard crust. Repeated fluctuations in the water table level add to the thickness of the iron crust. Bog ore is red in color, and has a tabular, pisolithic, nodular, laminated or irregular aggregate form.
In central Pennsylvania, deposition of limonite ore above the Gatesburg Formation was generated under anaerobic, acidic conditions and precipitated along the top of this formation. Also, iron can be put into solution, say for instance, in a swamp here decaying organic material creates reducing environment, a low pH (acidic) condition. As the swamp water naturally percolates downward, the iron is transported to the bedrock. Here at the soil / rock interface it comes into contact with an alkaline carbonate surface where the iron precipitates along joints to build up into massive, irregular limonite forms. If the iron-carrying groundwater enters a large cavity, cave, the iron can deposit on the surface of stalactites and become incorporated into the limestone as an iron carbonate mineral.
Siderite (iron carbonate) is an iron ore mineral that composes beds or nodules that form during precipitation or as an alteration of preexisting carbonate concretions. The factors influencing their formation of iron sulfide or iron carbonate precipitation include the action of bacteria, the amount of marine sulfate in the sediment and a source of carbon is needed. Iron carbonate nodules or concretions generally form in deltaic or brackish water.
Siderite has been found in bogs and marshes. It forms around fragments of wood of metal or may form where there is a deficiency of sulfate. Siderite precipitates in the interstices of sediment incorporating the silt/clay particles within the concretion
Blackband ore is a siderite layer adjacent to a bed of peat is. The blackband siderite deposits require a low-sulfate, anoxic water chemistry.
Meteoric water is water slightly acidic, containing humic acids and carbonic acid, the ph is usually as low as 4.0 – 5.0 and it is oxidized. Weathering occurs when meteoric water attacks the minerals within the bedrock. Meteoric water can oxidize, hydrate and carbonize rock-forming silicate minerals. The interaction of meteoric water and carbonate rocks leads to the dissolution of limestone and dolomite. Residual minerals are left behind that were incorporated in the carbonate rock at the time of deposition. During normal weathering conditions, exposure to meteoric water leads to the removal of alkalies and alkali earths, sodium, potassium, calcium, and magnesium from the residual soil developed on the bedrock.
Almost to Collecting Site
Mineralized Layer
We continued along the rail bed until at last a tall rock layered cliff was in front of us. Within the rock layering we see the famous limestone of Pennsylvania, a coal vein of several inches in height and finally what they were looking for, the iron ore layer. This particular deposit could be found up to a foot in thickness.……iron ore. With much excitement and enthusiasm we pull out a streak plate. Holding their breath, the test confirms the ore to be hematite. We gather a number of specimens and load our back packs. After exploring the area, photo taking and a short break we begin their return trip following the railroad tracks back.
About a mile into their return trip we come across a hiker also walking the tracks coming in our direction. Naturally we all stop and chat, talk about their recent find. The hiker not so intrigued states “So, you’ve dug up some iron, the hills are full of it, so what”? Me being not only being in love with rocks but also a history enthusiast, especially local history, was slightly shocked with the hiker’s response. I would like to tell you a story if you have the time, I said to the hiker. We sat in the shade and I began……
Red Hematite
Streak Plate
Native iron rarely if ever exists in a pure state on the surface of the earth. How do we know that? Elemental iron is highly reactive to oxygen and or water especially saltwater. But, there are a few exceptions, meteoritic iron contains a high percentage of iron and can be found in small amounts all over the planet. The Hoba Meteorite, a sixty ton specimen fell to Earth and remained intact eighty thousand years ago. Then there are the massive blocks of native iron and iron carbide, weighing up to 22 tons, found at Uivfaq, Disko Island, Western Greenland. The iron blocks are associated with tertiary basalts that erupted during rifting between Greenland and Baffin Island, early in the opening of the Davis Strait. The iron is an assemblage of iron and iron carbide (cohenite). These boulders were found by a Swedish expedition, led by A. E. Nordenskiold, in 1870. Recently a new iron boulder was found in August of 1985 in Stordal about 70 km from the first find.
Happy Hunting
Frank
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