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University of Louisiana at Lafayette
Heavy Mineral Applications in Sedimentary Petrology Advanced Sedimentary Petrology, Fall 2013
Shanna Mason 11-‐18-‐2013
Abstract
Heavy Mineral analysis in sedimentary petrology is both important and precarious at the same time. The unique physical characteristics that enable their importance can also lend to their detriment. The applications of heavy minerals in sedimentary petrology are discussed within this text in two sections. The first, dealing with applications of heavy minerals in
modern depositional systems, and the second discussing provenance applications. Heavy Mineral analysis in modern depositional systems has had a plethora of research centering on hydraulic equivalents. One of the most prominent studies by Gordon
Rittenhouse analyzed heavy minerals in modern sedimentation problems of the Rio Grande. However, his research was negated through many other studies.
Provenance determination in terms of heavy minerals occurring in sediments must have the depositional environment considered carefully. Due to the unique physical characteristics of
heavy minerals, their occurrence in any assemblage is depending on their stability. Through analysis of multiple research studies on the applications of heavy minerals, it will be evident how their unique characteristics can be detrimental to their analysis. However, with an understanding of the sediment history, this text will prove through various studies that petrologists can compensate for these variables, strengthening the importance of heavy
mineral analyses.
INTRODUCTION
Heavy minerals, the fraction of a sandstone comprised of many different mineral grains with
specific physical and chemical characteristics, have long been recognized as an important
indicator of the parentage and history of sediments within a depositional environment (Briggs,
1965). The amount of research on accessory minerals, as they are also called, available for
discussion is immense. Given the early popularity of heavy mineral analysis, the recent decline
in their use gives reason to analyze the cause. This decline is, in part, due to technological
advances, but it is also due to the general realization of their susceptibility to the processes of
transport, deposition, and diagenesis. However, by assessing the history of the sediment,
analysis of these minerals can be enhanced by compensating for their environmental variables
in various ways (Bateman, 2007). This paper will focus on applications of heavy minerals in
sedimentary petrology in two sections. First their application in modern depositional systems,
and various studies conducted, will be discussed, then heavy mineral analysis in terms of
provenance. Showing how, through research, we can identify the weaknesses of heavy minerals
in certain environments and use this knowledge to improve the accuracy of their use.
Unfortunately, every application of heavy minerals in sedimentary petrology cannot be
discussed. The application of heavy minerals can expand well into other areas besides modern
depositional systems and provenance. Subsurface correlation of mineral zones, tectonic history
determined by heavy mineral analysis, and varietal studies of many other species besides
tourmaline all indicate promise towards research in the field of heavy mineral analysis that can
only add to its value.
HEAVY MINERALS IN MODERN ENVIRONMENTS
FLUVIAL SETTINGS
Much of the research dealing with heavy mineral analysis in modern depositional systems has
centered on Hydraulic Equivalents. Beginning in 1933 with William Rubey, who coined the term
‘hydraulic equivalence’ to show how minerals with different physical properties can be the
result of the same hydraulic conditions. These hydraulic equivalents were calculated using
settling velocities of heavy minerals according to Stokes Equation (see fig. 1). Stoke’s Law states
that settling velocities of spherical particles are a function of particle diameters, effective
densities, and inversely as the viscosity of fluids (Rubey, 1933). Rubey determined that the
equation outlined in figure 1 worked for particles between the diameters of 0.0002 and 0.2
millimeters. For larger particles, hydraulic equivalents will deviate until quartz particles reach
1.5mm in size, at which point fall velocities will be proportional to the square root of diameter
particles (Rubey, 1933; Tourtelot, 1968). The hydraulic equivalents of quartz, magnetite, silver
and gold, calculated by Tourtelot (1968) using the values from the equations outlined by Rubey
can be seen in Figure 2. Even though Rubey did not use his work to analyze depositional
environments, Rittenhouse knew that it could be (1944).
In his study on the modern sedimentation problems of the Rio Grande River,
Rittenhouse figured out an empirical way to assess source areas on different streams in the
Middle Valley using the Hydraulic Ratio. Between 1936 and 1941, the Rio Grande and the
tributaries that feed it, were depositing around 12,000 acre-‐feet of sediment per year. This
caused multiple issues such as; the channel and floodway capacity to discharge flood waters
was diminished, the ground-‐water table had been raised, infertile sands were being deposited
onto pastures and cultivated land, and accelerated soil erosion was occurring in relation to
channel aggradation (Rittenhouse, 1944). In conjunction with the Soil Conservation Service in
Greenville, South Carolina, Rittenhouse set out to tackle the sedimentation problems by using
heavy mineral analyses to figure out which tributary was depositing the most sediment so that
controls could be implemented to stop damage from continuing to occur. He took the hydraulic
equivalent size, determined by Rubey, and calculated a ratio that he believed to be more
reliable than other quantitative methods. The Hydraulic Equivalent sizes calculated
experimentally from two sites of the Rio Grande experiment is outlined in Figure 3. Rittenhouse
defined the Hydraulic ratios as “100 times the weight of a mineral in a known range of sizes,
divided by the weight of light minerals of equivalent hydraulic size (Rittenhouse, 1943: 1725).”
Rittenhouse said that when the hydraulic ratio is used, it helps to eliminate variations in
assemblage caused by hydraulic selectivity, or the selectivity of a stream to deposit all the
heavy minerals in the bed load (Briggs, 1965). Multiple analyses concerning the size distribution
of heavy minerals have since occurred, offering varying validity opinions of this method.
Rittenhouse based the Hydraulic Ratio on the constant relative availability of the heavy
minerals along a transverse section of a stream. During an investigation of sediments in the
Rhine River, Van Andel rejected this basis of constant availability, stating that this did not apply
to his area of study (1959). The negation of the basis of hydraulic ratios puts the validity of
Rittenhouse’s theory in question. If it cannot be applied elsewhere, it is of no use to
sedimentary petrologists (Young, 1966). Edward Young conducted a study of four quantitative
methods used in heavy mineral analysis using two samples from Rittenhouse’s Rio Grande
study. He discounted the hydraulic ratio method in part due to the laboriousness of
calculations, but also due to relative deviation results (see fig. 4). Rejecting the hydraulic ratio
method, Young obtained results favoring the weighted number percentage and weight
percentage methods for heavy mineral analysis (Young, 1966). Louis Briggs also called into
question the validity of Rittenhouse’s argument, postulating that modal separation of heavy
and light minerals increases with grain size for samples with diameters larger than 0.125mm.
He also determined that the frequency of any mineral in a sandstone depends on interactions
between minerals with different specific gravities, particle shape, availability of size to transport
mechanism, and the hydraulic selectivity of the agent (Briggs, 1965). White and Williams (1967)
studied the settling velocities of light and heavy minerals in cross bedding. Determining that
settling velocity equivalents varied between bottomset and foreset laminations due to
deposition, which can be resolved into components of suspension and traction loads (White
and Williams, 1967). Variations from hydraulic equivalent sizes can also be found when looking
at studies that focus on lacustrine and coastal depositional settings.
COASTAL AND LACUSTRINE SETTINGS
In 1959, Donald McIntyre attempted to relate the hydraulic equivalent sizes determined by
Rubey to Lake Eerie foreshore deposits. The deposits to be sampled occurred in alternating
light and dark layers that were called “lenses.” Three separate lenses were sampled and
categorized as layers A, B, and C. Hydraulic equivalent quartz sizes were then compared for five
present heavy minerals in each layer using both quartz and garnet as the basis. The accuracy of
calculated hydraulic equivalent sizes varied within each layer. The variances can be seen when
looking at Figure 5, which describes hydraulic equivalences obtained either by calculations or by
subtracting the mean grain size of quartz or garnet from the mean grain size of each of the
heavy minerals in the same layer. Using quartz as the basis, only the C layer came close to the
theoretical values. For values of the A and B layers, hydraulic sizes using quartz taken from the
samples were continuously greater than the calculated sizes. However, when garnet was used
as a base, calculated hydraulic equivalent sizes more closely related to those observed in the
samples (Mcintyre, 1959). Looking at this experiment and the numerical values exhibiting
deviations from hydraulic equivalent sizes, it is evident how subjective to environmental
conditions hydraulic equivalents are.
Bryce Hand (1967) set out to determine hydraulic equivalents using settling velocities in
his study that examined sand samples from beaches and dunes along a strip of the New Jersey
coast. Hand thought that beach deposits should mimic hydraulic equivalence theory laid out by
Rubey and Rittenhouse, because they are both deposited by a fluid medium (Hand, 1967). The
determination of his study was that the correlation was incorrect. His results showed that
actual settling velocities related to lower hydraulic equivalents sizes more so than their
calculated equivalents, which is outlined by figures 6 and 7 that show cumulative percentage
curves according to settling velocities. Hand attributed this to the stability of heavy minerals
and their ability to withstand various conditions in a deposit relative to their light mineral
counterpart. He uses the example of quartz and garnet to illustrate this point. Showing that to
make garnet and quartz actual equivalent counterparts, you must decrease the settling velocity
of garnet slightly to account for its ability to remain in a deposit longer than quartz (Hand,
1967).
These significant studies on heavy minerals, and their hydraulic equivalent sizes as seen
in modern deposition, show the amount of variation present in each environment. In some
cases, heavy minerals can be very useful in modern sedimentation problems. They can also
enable us to understand hydraulic conditions acting on various sediments loads more than light
minerals can. However, their physical characteristics lend the need for unique knowledge on
how they react in each environment. Petrologists must take a second look at their reactions to
transportation and depositions mechanisms to ensure each variable is accounted for in
quantitative analyses, leaving more space for error.
HEAVY MINERALS AND PROVENANCE
PROBLEMS WITH HEAVY MINERAL ANALYSIS IN PROVENANCE DETERMINATION
Historically, heavy mineral analysis has been most widely used by Petrologists as provenance
indicators (Briggs, 1965). Their unique physical characteristics and lesser abundance in
sedimentary rocks than light minerals give them a distinct advantage in the determination of
source rocks (Blatt, 1985). However, these unique characteristics can also be their downfall.
The declination of heavy mineral applications in sedimentary petrology in the last 20th century
is due to the revelation that these minerals are specifically more apt to post-‐depositional
processes (Van Andel, 1959). Therefore, many variables must be considered when using heavy
mineral analyses. Recent research of these variables suggest that when considered correctly,
these variables can be used to attribute to the accuracy of heavy mineral analysis rather than
take away from it. Here we will discuss how research surrounding the post-‐depositional
alteration of heavy minerals can be applied in a way that aids in the accuracy of their analysis,
then we will look at one of the many important stable minerals and its applications in
provenance determination.
Richard Bateman and John Catt (2007) identified five phases of the sedimentary cycle
that can affect a heavy mineral assemblage, and processes within each one that particularly
have an impact. They use an approach designed to compensate for the specific sedimentary
history of an assemblage in the determination of the parent rock. To do this, they examine the
various processes identified in each phase of the sedimentary cycle. By understanding the
processes they intended to show (1) the value in applying multivariate statistical techniques to
identify trends of heavy mineral data and (2) to demonstrate the value of heavy mineral data
when accompanied with other paleoenvironmental data analysis. They published research on
five case studies and the implication of the identified modifying processes on provenance
identifications in tertiary and quartenary deposits found in the British Isles (Bateman, 2007:
153). During their analysis they claim that the provenance interpretation ability of heavy
minerals is so unique that it is worth the research surrounding post-‐deposition alteration
processes, because most of them are predictable and can be compensated for in some fashion.
STABILITY OF HEAVY MINERALS IN PROVENANCE DETERMINATION
The composition of a heavy mineral assemblage must be analyzed with the various physical and
chemical processes that were active post-‐deposition of the sediment. The appearance of any
heavy mineral in an assemblage is the direct result of its ability to withstand abrasion during
transport, weathering, and diagenesis after deposition (Pettijohn, 1942). The stability of an
accessory mineral, or its ability to resist alteration, has been analyzed by a variety of authors,
each one determining an “order of stability” to interpret the presence of certain minerals in an
assemblage. This stability factor is controlled by pressure, temperature, connectivity and PH
level of pore fluids, presence of oil, variation in the mineral’s chemical composition, and the
amount of time the sediment spent in deep burial. Pettijohn, in “Sedimentary Rocks,”
illustrated the most notable authors to determine orders of stability, both in terms of
weathering and intrastratal solution, which is outlined in Figure 8. The research behind the
progressive stability of heavy minerals overtime led to the development of the Zircon-‐
Tourmaline-‐Rutile index.
Zircon, Tourmaline, and Rutile, all heavy minerals that are very mechanically and
chemically stable, have been shown to concentrate with quartz as sandstones become more
quartzose. Therefore, it has been determined that grains of these heavy minerals can be
composed into an index that progresses amongst various sandstone classifications (Hubert,
1962). This index can then be correlated to other samples to determine the depositional
environment that created the sediment in question. As the index of these minerals increases, it
is also noted that other transparent heavy mineral presence decreases. Which is why Hubert
proposed this ZTR index as an indication of the “maturity” of sandstone, in his interpretation
meaning the degree to which the sediments had been modified. The index ranges from low
values in arkoses and graywackes, to over 90% in most orthoquartzite sandstones (Hubert,
1962).
In contrast to compensation of variables involving intrastratal solution, Van Andel (1952)
proposed that in some cases the absence of unstable minerals was instead the result of
processes occurring prior to deep burial. To account for this, heavy mineral analysis used in
provenance determination of basins must look at regional heavy mineral distribution. This
regional province method required the inclusion, interpretation and sampling of multiple
geographic regions. Van Andel applied this theory to the Rio Grande in which he argued the
importance of the applicability of heavy minerals in sedimentation analysis. Flores and Shideler
(1978) supported this theory as well in their analysis of the same region, concluding that
selective decomposition, determined by the ZTR index, did not contribute to regional variations
in the Rio Grande (Flores, 1978).
TOURMALINE
Krynine (1946) studied the application of Tourmaline and its multiple varieties in provenance.
He outlined 5 major types of provenance producing Tourmaline, and the subsequent varieties
that are characteristic of each. Due to its high geochemical stability, Tourmaline can withstand
ranges of temperatures and pressures. Varieties of Tourmaline are not only applicable as an
index guide in primary occurrences, but also as reworked sediments. Krynine notes that
Tourmaline can survive multiple sediment cycles, depending on the variety. Also notable is the
authigenic occurrence of Tourmaline. As a secondary mineral, its occurrence is widespread and
therefore predictable over a geographic range. Tourmaline varietal studies can be applied to
provenance determination, such as the identification of the Gatesburg formation as the parent
rock of the Bellefonte Sandstone. They can also be applied in determination of the tectonic
history of a formation, such as the Tuscarosa Quartzite in relation to the Appalachian
Geosyncline in East Central Pennsylvania. More information on both of these determinations
can be found in Paul Krynine’s work “The Tourmaline Group in Sediments,” published in the
Journal of Geology in 1946.
CONCLUSION
Even though the unique physical characteristics that comprise a heavy mineral assemblage
leads to their environmental weaknesses, it is also those characteristics that enable them to be
of such value to sedimentary petrology. Applying knowledge gained through the research of
their susceptibilities to their analysis in varying applications can actually benefit their use.
However, this does require careful analysis of the geochemical and physical properties present
in a sample and how they relate to the sediment history.
REFERENCES
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Superficial Deposits, with Particular Reference to Post-‐Depositional Modification of
Heavy Mineral Assemblages, in Heavy Minerals in Use, eds., Mange, M. and D. T. Wright,
Oxford, Linacre house, 151-‐188 p.
Blatt, H., 1969, Intrastratal Solution and Non-‐Opaque Heavy Minerals in Shales, Journal of
Sedimentary Petrology, v. 39, no. 2, p. 591-‐600.
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South Texas Outer Continental Shelf, Gulf of Mexico, Journal of Sedimentary Petrology,
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Hand, B. M., 1967, Differentiation of Beach and Dune Sands, Using settling Velocities of Light
and Heavy Minerals, Journal of Sedimentary Petrology, v. 37, no. 2, p. 514-‐520.
Hubert, J. F., 1962, A Zircon-‐Tourmaline-‐Rutile Maturity Index and the Interdependence of the
Composition of Heavy Mineral Assemblages with the Gross Composition and Texture of
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!Stokes!Law!of!Settling!Velocities!
! = ! !18�!!!! − !!!
! !!! = !ℊ18 !�!
!! − !!!! !!! !
Where:!! ! ! ! ! ! ! Magnetite!Example:!!ν!=!Fall!Velocity!! ! ! ! ! !g!=!gravity! !!!!=!Specific!Gravity!of!Quartz!Grain! !!!=!2.66!!! = Specific!Gravity!of!Water! !! = 1.00!!! = Specific!Gravity!of!Magnetite! !! = 5.18!!! = Diameter!of!Magnetite!Grain! !!! =!Diameter!of!Quartz!Grain! !η!=!Coefficient!of!Viscosity!of!Water!(Constant!Under!Conditions)! η!=!1.00!
!
!
!
! !
!=(2.66−1.00)%↓'↑2
=(5.18−1.00) %↓*↑2 !
%↓* =,√1.66/4.18 , %↓' =0.63
%↓' !
Only!MagneLte!grainns!0.63!
mm!in!diameter!will!fall!with!the!same!velocity!as!Quartz!
Grains!1.00!mm!in!diameter!
Hydraulic!Equivalent!of!Magnetite!
Figure!1:!(modified!from!Rubey,!1933)!
Figure 2: (From Rittenhouse, 1944) Figure 3: (from Tourtelot, 1968)
Figure 4: (from Young, 1966)
Figure 5: (from McIntyre, 1959)
Figure 7: (from Hand, 1967) Figure 6: (from Hand, 1967)
Figure 8: (from Petitjohn, 1975)