GEOCHEMICAL ANALYSIS OF THE IRON-ENRICHED SOIL OF MEHERRIN, VIRGINIA

Sara Irena Chojna1, Arif M. Sikder1, Jose Brum2, Xin-Chen Liu1, Elizabeth Keily1, Dustin M. Clifford3, Carlos E. Castano Londono3

1. Center for Environmental Studies (CES); Virginia Commonwealth University (VCU),

1000 West Cary Street, Richmond, VA 23284

2. Olympus Scientific Solutions Americas, 48 Woerd Ave, Suite 105, Waltham, MA 02452

3. Nanomaterial Characterization Center (NCC),Virginia Commonwealth University (VCU)

620 West Cary Street, Richmond, VA 23284

Meherrin is located in the Piedmont region of Virginia. The Piedmont region is at the foot of the Blue Ridge Mountain range, which is part of the Appalachian Mountain system. The Piedmont

features rolling hills and deeply weathered bedrock.

• Most of the igneous and metamorphic rocks in the province range in age from Proterozoic to Paleozoic. They form the internal core of the Appalachian Mountain belt.

• Triassic sedimentary rocks, diabase dikes, and basalt flows are present in several grabens and half-grabens that formed during rifting associated with the opening of the Atlantic Ocean.

• Rivers and streams carrying sand, silt, and mud flowed into these lowland rift basins, burying swamps and marshes and later producing small coal measures.

Geology of the Piedmont Region

Sampling Locations• Site “MA” consists of

Lloyd Clay Loam and not prime farmland.

• Site “MB” consists of Iredell Loam and farmland of state-wide importance.

• Site “MC” is a bit southwest of our site in Keysville, VA. It is much like site “MA.”

Area Soil Description

There is a strip of land, running almost in the

center of the county about 10 miles in width that

has stiff red soil.

Stream clay is known to occur one mile

southwest of Meherrin. Between Meherrin and

Keysville (also Southwest), the town of Simplicity

has pre-Cambrian volcanics that yield a residual

clay 3 to 4 feet in depth.

• Northeast of Meherrin, the soil consists of a yellow to brown decomposed granite with streaks and patches of red.

• The soil in the county is generally fertile, but the ridges are thin and poor. The lower eastern part of the county is a light gray or sandy soil.

Area Soil Description

• There is a strip of land, running almost through the center of the county, that is about 10 miles wide and has stiff red soil.

• Stream clay is known to occur one mile southwest of Meherrin. Between Meherrin and Keysville (also Southwest), the town of Simplicity has pre-Cambrian volcanics that yield a residual clay 3 to 4 feet in depth.

Meherrin Soil

• Meherrin consists of fine cut residual clay that is 18-feet deep. It is red and fairly sticky. The soil in this image (left) is from site “MA.”

MA: color red (10R 4/8) MB: color green (10Y 5/2)

The samples from each site were collected by core sampling at 6-inch intervals. For this study, sites were coded as MA, MB, and MC and located within 3 miles of each other.

MA and MB differ considerably in their color.

Aim and Objective• Consisting of Ultisols of the Georgeville series, Meherrin’s soil has a high

amount of clay (27%) in comparison with the rest of the Georgevilleseries.

• A geochemical analysis was conducted to understand the differences of the soil characteristics in Meherrin, with respect to the nearby soils of the Piedmont region.

• Several nearby sites have been assessed for comparison.

Analytical Approach• Samples were size partitioned by wet sieving.

• The sample fractions, less than 63 microns and greater than 63 microns, were analyzed by an X-ray fluorescence (XRF) spectrophotometer to understand elemental composition, soil color, and properties.

• After thoroughly washing and drying the greater than 63-micron fractions, magnetic particles were manually separated using a strong hand magnet, and the composition was studied using XRF.

• Separated magnetic particles were analyzed with an Olympus® TERRA® X-ray diffraction (XRD) analyzer.

• A scanning electron microscope (SEM) was used for micromorphological and elemental analysis.

Result of Elemental Analysis by XRF• The Fe₂O₃ content in bulk samples is relatively high, varying between 10% and

30%.

• The concentration of Fe₂O₃ increases with depth in samples for location MA, yet the highest concentration is observed in the most shallow samples.

• In all locations, the distribution of alkali metals does not show a trend.

• Chemical index of alteration (CIA): 100–80 is highly weathered; 60–80 is glacial to moderate; below 60 is a cold glacial environment.

• CIA values between 50 and 60 indicate incipient weathering, between 60 and 80 indicate intense weathering, and more than 80 for extreme weathering.

Result of Elemental Analysis by XRF

CIA=(Al2O3/Al2O3+CaO*+Na2O+K2O) × 100

Distribution of Magnetic Particles

Distribution of Magnetic Particles

Sample ID

Bulk Dry

Weight

(gm)

Fractions > 63

um (gm)

Fractions > 63

um (wt%)

Magnetics >

63 um (gm)

Magnetics

> 63 um

(gm)

200a 21.51 8.86 41.19014412 0.12 1.35440181

200b 8.75 5.73 65.48571429 0.09 1.57068063

200c 160.12 35.67 22.27704222 0.44 1.23352958

400a 21.61 13.64 63.11892642 0.22 1.61290323

400b 37.73 17.3 45.85210708 0.21 1.21387283

400c 90.81 15.39 16.94747275 0.23 1.49447693

800a 89.24 23.85 26.72568355 0.32 1.34171908

800b 46.47 23.66 50.91456854 0.66 2.78951817

800c 40.68 23.5 57.76794494 0 0

1600a 35.83 17.97 50.15350265 0.89 4.95269894

1600c 47.44 12.82 27.02360877 0 0

More Results of Elemental Analysis

Mineralogical Analysis by XRD

MA7: Kaolinitic MB5: Much less clay mineral

XRD Analysis of the Magnetic Particles:Cobalt Target

XRD Analysis of the Magnetic Particles:Cobalt Target

• 11% akaganeite: akaganeite is formed by the weathering of pyrrhotite. The occurrences in meteorites and lunar samples are thought to have been produced by interaction with Earth's atmosphere.

• 51% magnetite and 29% hematite: the mineral form of ferric oxide iron(III) oxide (Fe2O3) is one of several iron oxides. Only 1% goethite is an iron oxyhydroxide containing ferric iron. It is the main component of rust and bog iron ore.

SEM Analysis of Magnetic Particles

SEM Analysis for Magnetic Particles

Widmanstӓtten Pattern

SEM EDS Analysis

ObservationsMicroscopic analysis of separated magnetic particles reveals the presence of well preserved euhedral crystals of magnetite, hematite, and potentially wustite (cubic

FeO). Furthermore, the SEM analysis revealed magnetic spherules and relic grains with apparent Widmanstӓtten patterns. Such patterns may indicate an extra-terrestrial or

volcanic source of iron-enriched mineral phases, accountable for the special characteristics of Meherrin soil.

Acknowledgements

VCU Center for Environmental Studies

Dr. Rodney Dyer

Dr. Leigh McCallister

Jen Ciminelli

Mack Barnes