F o r m a t io n A n d O c c u r r e n c e s O f L a u m o n t it e A n d R e l a t e dM i n e r a l s In T h e C a r o l in a s A n d V ir g in ia ,

M id d l e M e s o z o ic Z e o l i t e F a c ie s M e t a m o r p h is m , S o u t h e r n A p p a l a c h ia n P ie d mo n t

D o n a l d R . P r iv e t t , P .G . S .T .A . R . E n v ir o n m e n t a l

1 C ir c l e S t r e e t G r e a t F a l l s , S C 2 9 0 5 5

Presentation Time: AM 11:40 AM-12:00 PM

drprivett@gmail.comSoutheastern Section

60th Annual Meeting (23-25 March 2011) Session No. 4

Piedmont Geology: New Mapping and New Perspectives

Wilmington Convention Center: Room 106

A 175 -195 Ma hydrothermal zeolite grade metamorphic event

altered most pre-Jurassic rocks

Southern Appalachian Piedmont

Central Georgia, South and North Carolina to Virginia

file:///Users/donprivett/Desktop/laumontite/PRVTT Fig1 Previous Laumontite 1.jpg

a

Zeolite grade thermal metamorphismZeolite grade thermal metamorphism

Zeolite facies represents

All mineral, textural and chemical changes resulting

from hot waters, steam or/and gas

crystallization of fracture – filling and replacement

zeolites and prehnite in host rocks

GENERAL GEOLOGY

Area Neoproterozoic and Paleozoic igneous, metamorphic, and Triassic igneous

and sedimentary rocks

altered by period of zeolite grade regional thermal

metamorphism

Event evidenced by the laumontite filling fractures and replacing feldspars in intrusive

and in older metamorphosed diorites and granites.

Laumontite identified from over 100 separate locations

in relatively unweathered outcrops rock exposed in foundations, trenches, quarries, mined caverns and in cores from borings for power plants and cuttings from water wells and exploratory test wells.

LAUMONTITE DISTRIBUTION

OCCURRENCE

Laumontite occurs as:

(1) single pink and white euhedral crystals in druses and incompletely filled veins

(2) veinlets of matted interpenetrating crystal aggregates filling single and multiple narrow fractures and joints

file:///Users/donprivett/Desktop/laumontite/scan0069.jpg

file:///Users/donprivett/Desktop/laumontite/Untitled_003.jpg

Biotite - microline granite porphyry cut by numerous pink

asicular laumontite veinlets.

Laumontite-calcite veinlet cutting altered diorite.

Interpenatrating asciular laumontite crystals on fracture in diorite

file:///Users/donprivett/Desktop/laumontite/lau21.tif

(3) replacement of plagioclase forming partial to complete "mosaic pseudomorphs" composed of minute laumontite crystals and albite.

Laumontite is best identified by microscopic study.

file:///Users/donprivett/Desktop/laumontite/microlaumrpplag.jpg

A. in diffuse plane light laumontized plagioclase displays a mottled texture

file:///Users/donprivett/Desktop/laumontite/lau21.tif

B. polysynthetic twinning of plagioclase is destroyed, partly replaced plagioclase retains its twinning; however, it is mottled top plane light, same cross polars

file:///Users/donprivett/Desktop/laumontite/tscalc copy.tif

Calcite and radiating laumontite

Calcite and radiating laumontite

file:///Users/donprivett/Desktop/laumontite/scan0003crop.tif

radiating laumontite veinlet

Larger laumontite crystals, crossed polars.

Mixed calcite laumontite crossed polars

2

Field exposure in saprolite/partialy weathered quartz monzonite - extensive laumontite

replacement and veins white laumontite leonardite-Compass for scale

ZEOLITE PARAGENESISLaumontite and other zeolites

theoretical and experimental limit determinations and detailed paragenesis studies yield

considerable disparity between theoretical and experimental temperature and pressure limits

and substantially lower temperatures of natural formation.

(Coombs,1952, Thompson, 1971, Frost, 1980 and Loui, 1971) (Boles and Coombs, 1977 and Suranam, 1973).

PARAMETERS THOUGHT TO CONTROL TEMPERATURE AND PRESSURES OF

NATURAL ZEOLITES IN ROCKS

Experimentally determined temperatures are both higher and lower than values obtained under

natural conditionsFluid pressure gradients activities of CO2, pH2Oratio of water and CO2

the permeabilitynucleation and reaction kinetics

oxygen fugacity presence of additional ions all

can alter the temperatures of formation Boles and Coombs (1977)

Laumontite Stability Limits Vary Widely

upper limits of 230º – 325º at 0.5 kb, 250º at 2.75 kb. Thompson (1971) Loui (1971)

lower limit even greater conflict compared 150º - 200º C at 1 kb where p = p (Loui, 1971) lowest recorded temperature of

formation 43º C crystallized at Suspe Hot Springs, California.

In buried sedimentary rocks estimates of 50º C laumontite - 90º C for prehnite (Boles and Coombs, 1977)

75º + 5° C for laumontite in hot springs (Castino and Sparks, 1974, Siki, 1969 )

calcite fluid inclusions in laumontite filled amygdules of lava flows, Iceland 140º - 200º C. Meghan, Robinson and Delaney (1982)

Zeolites occur in

geothermal areas of Iceland a.

in California metamorphic rocks b.

New Zealand thermal areas c.

Southeastern Piedmont U.S.A.

a. (Kristmannedottir and Tomanson,1978), (Mehegan, Robinson and Delaney, 1982) b. (Madsen and Murata, 1970) c. (Barnes, 1977)

Laumontite present in the majority of rock exposed in the Piedmont

gneiss of the Inner Piedmont

metamorphosed and unmetamorphosed igneous rock

metasedimentary rocks of the Charlotte Belt and the

Kings Mountain Belt

metavolcanic and metasedimentary rock Carolina Slate

Belt and in

Buried Triassic - Jurassic sedimentary and igneous rocks

discovery of laumontite in buried Triassic rocks - cored basement below the Triassic of South Carolina and south central Georgia suggest that laumonatization is even more extensive laumontite fills amygdules and replaces plagioclase in a 184 +/- 3 my basalt from Dorchester county, S.C. (Gottfried et.al.,1983)

present in Triassic sedimentary and older igneous rocks from South Central Georgia (Chowns and Williams,1983)

Laumontite imparts a pinkish color to the altered and replaced plagioclase.

appears to be directly proportional to the intensity of laumonatization laumontite and calcite fill vein interiors

x-ray reflections vary with the relative humidity material is best described as laumontite-leonhardite. Laumontite readily dehydrates to leonhardite unless the sample is kept under conditions of 100% relative humidity

Pangea breakup

Tectonic activity about 170 -150 mya - Triassic and Jurassic separation of North

America and Africa

fractured old weaker shears, formed new joints and faults.

ORIGIN

SUMMARYHeated circulating groundwaters mixed with hydrothermal

solutions fluids

reacted with plagioclase prehnite and laumontite.

Excessive calcium reacted with silica to produce the fracture filling laumontite, calcite other lower temperature zeolites.

Two generations of diabase dikes are evident; suggesting that igneous activity persisted as the stress changed.

zeolite grade thermal alteration metamorphism is widespread in rocks of the southern Appalachian rocks.

Immature clastics deposited in subsiding half grabens

generation of basaltic magmas

basalt flows in Triassic sedimentary rock

intrusion of diabase dikes and basaltic to diabase sills.

.

Thank You – Have a great day