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Corresponding author: e-mail, bvangose@usgs.gov

Abstract

Ancient and modern types of sedimentary placer deposits formed in both alluvial and coastal environments have been signficant sources of the rare earth elements (REEs). The REE-bearing minerals in placer-type deposits are primarily monazite [(Ce,La,Nd,Th)PO4] and sometimes xenotime (YPO4), which are high-density (heavy) minerals that accumulate with the suite of heavy minerals. Monazite has been extracted from many heavy mineral placers as a coproduct of the economic recovery of associated industrial minerals, such as titanium oxide minerals (ilmenite, rutile), zircon, sillimanite, garnet, staurolite, and others. Xenotime has been produced from some alluvial deposits as a coproduct of tin (cassiterite) placer mining.

Placers are mineral deposits formed by the mechanical concentration of minerals from weathered debris. Placers can be classified as eluvial, alluvial, eolian, beach, and fossil (paleo) deposit types. Monazite-bearing placer-type deposits can occur in residual weathering zones, beaches, rivers and streams, dunes, and offshore areas. The detrital mixture of sand, silt, clays, and heavy (dense) minerals deposited in placers are derived primarily from the erosion of crystalline rocks, mainly igneous rocks and moderate- to high-grade metamorphic rocks (amphibolite facies and higher). In fluvial settings, slope is an important factor for the concentration of heavy minerals from detritus. In coastal settings, the actions of waves, currents, tides, and wind are forces that concentrate and sort mineral particles based on size and density.

Placer deposits containing monazite are known on all continents. In the past, by-product monazite has been recovered from placers in Australia, Brazil, India, Malaysia, Thailand, China, New Zealand, Sri Lanka, Indonesia, Zaire, Korea, and the United States. More recently, monazite has been recovered from coastal and alluvial placers in India, Malaysia, Sri Lanka, Thailand, and Brazil. In particular, along the southwestern and southeastern coasts of India, beach deposits rich in heavy minerals have experienced renewed exploration and development, partly to recover monazite for its REEs as well as its Th, to be used as a nuclear fuel source.

Exploration designed to locate heavy mineral placers in coastal environments should identify bedrock terranes containing abundant high-grade metamorphic rocks or igneous rocks and identify ancient or modern coastal plains sourced by streams and rivers that drain these terranes. Trace elements associated with heavy mineral placers, useful as pathfinder elements, primarily include Ti, Hf, the REEs, Th, and U. Radiometric methods of geophysical exploration are useful in discovering and delineating deposits of heavy mineral sands. Several minerals in these deposits can produce a radiometric anomaly, but especially monazite, due to its high thorium content. Some beach districts in India and Brazil have been demonstrated as areas of high background radiation with potential dose exposure to humans and others, primarily due to the Th and U in detrital grains of monazite and zircon.

Monazite- or xenotime-bearing placers offer several advantages as sources of REEs. Ancient and modern deposits of heavy mineral sands that formed in coastal settings can be voluminous with individual deposits as much as about 1 km wide and more than 5 km long. Grains of monazite or xenotime in placer deposits are mingled with other heavy minerals of industrial value. Monazite and xenotime are durable and often the heaviest minerals within the sand-silt deposit, which makes them relatively easy to mechanically separate. Thus, the REE ore minerals, monazite or xenotime, can be recovered from heavy mineral placers as a low-cost coproduct along with the economic production of the associated industrial minerals.

Introduction

Alluvial and coastal placer deposits have been, and continue “o be, important sources of many mineral commodities, such as gold, tin (in cassiterite), titanium oxide (in ilmenite, rutile, leucoxene), and zirconium (in zircons), as well as additional ndustrial minerals (sand and gravel, sillimanite, garnet, staurolite, as examples). Placers are also sources of the rare sarth elements (REEs), chiefly via the minerals monazite (Ce,La,Nd,Th)PO4] and sometimes xenotime (YPO4). In fact, until the mid-1960s, when full-scale production of rare earths began at the Mountain Pass carbonatite deposit in southeastern California, placer mines recovering monazite as a coproduct were the world’s principal source of the REEs (Tse, 2011; Fig. 1).

Fig. 1.

Global map showing significant placer districts (red squares) that produced monazite and/or xenotime in the past or presently; these minerals were recovered as by- or coproduct commodities with other economic heavy minerals. Current monazite production occurs at modern beach placers in India and coastal placers at the Buena district, Brazil.

Fig. 1.

Global map showing significant placer districts (red squares) that produced monazite and/or xenotime in the past or presently; these minerals were recovered as by- or coproduct commodities with other economic heavy minerals. Current monazite production occurs at modern beach placers in India and coastal placers at the Buena district, Brazil.

With the increasing demand for REEs in modern technologies, combined with potential supply restrictions for specific REEs, placer deposits have reemerged as viable sources of rare earths, specifically through the recovery of monazite and/ or xenotime from placers composed of heavy mineral-rich sands. Presently, the purposeful recovery of monazite occurs from heavy mineral beach deposits mined and processed at several coastal sites along the southwestern and southeastern shores of India. These operations recover ilmenite, rutile, leucoxene, rutile, sillimanite, garnet, and sometimes other industrial minerals as primary commodities, and also separate monazite as a coproduct. The REEs within the monazite are extracted for sale, and the thorium (Th) in the mineral is sought as a fuel source for a nationally coordinated program in India to develop thorium-based nuclear power.

Ancient and modern coastal deposits of heavy mineral sands offer several advantages as ore deposits. As examples, these deposits are relatively easy to mine because they are weakly to poorly consolidated, and likewise are relatively easy to process. Examples of heavy mineral sands deposits are known on every continent and most likely also exist in Antartica. Ancient and modern deposits of heavy mineral sands that formed in coastal environments can be voluminous. Individual bodies of heavy mineral-rich sands are typically about 1 km wide and more than 5 km long. Many heavy mineral sands districts extend for more than 10 km, encompassing several individual deposits that are spread along an ancient or modern strandline. Reported thicknesses of economic deposits range from 3 to 45 m. Individual ore deposits typically comprise at least 10 million metric tons (Mt) of ore (the total size of the individual sand-silt body), with an overall heavy mineral content of 2 to >10%.

This paper describes examples of alluvial and coastal placer deposits known to host economic concentrations of monazite or xenotime (economic in the past or present). Descriptions of these deposits and their geologic setting provide insights into source rocks, transport mechanisms, and the depositional environments that form potentially economic REE placer deposits. Separately discussed is a classification scheme for placer deposits in general, followed by explanations of oregangue mineralogy and geochemistry characteristic of REE-bearing placers. These insights contribute to discussions on genetic models and exploration criteria relevant to monazite- or xenotime-bearing placers, particulary coastal placer deposits. Next, the aspect of radiation exposures from these deposits is discussed; relatively high levels of natural radioactivity, produced by monazite and zircon in some coastal sands, have been studied, particular in India. Finally, the significance of monazite-bearing placers is reemphasized—monazite in placers can contribute much-needed REEs to the global supply as well as thorium, obtaining the monazite (and/or xenotime) as a coproduct of the economic production of titanium oxide minerals, zircons, and other industrial minerals.

Terminology

Much of the terminology used to describe placer deposits is not commonly used in geologic discussions. To aid the reader and avoid confusion, some terms often used in discussions of this general deposit type are as follows.

“Heavy minerals” are generally defined as dense minerals that have a specific gravity greater than 2.85. For comparison, quartz has a specific gravity of approximately 2.65.

“Heavy mineral suite” is a term that refers to the entire group of heavy minerals identified within a particular deposit.

“Grade,” in reference to a heavy mineral sands deposit, most often refers to the average heavy mineral content of the deposit (usually reported in wt %).

As noted earlier, placers are sedimentary deposits formed by the physical-mechanical concentration of minerals orginally derived from weathered debris. Some of these deposits can contain economic (or potentially economic) concentrations of heavy minerals; in addition to “placer,” this deposit type is also commonly referred to as “heavy mineral sands.” In the context of this discussion, placer and heavy mineral sands are interchangeable.

General geology

Placers are mineral deposits formed by the mechanical concentration of minerals from weathered debris. Examples of placer deposits occur in beaches, rivers and streams, dunes and offshore areas. The economic minerals hosted by placer deposits are very resistant to chemical and physical breakdown (durable), and typically have high density. The detrital mixture of sand, silt, clays, and “heavy” (dense) minerals deposited in placers are primarily derived from the erosion of crystalline rocks. The source rocks include a wide variety of igneous rocks and moderate- to high-grade metamorphic rocks (amphibolite facies and higher), and some sandstones and conglomerates. This detritus is transported by mechanisms such as moving water and aeolian activity, carrying the dense minerals in a mixture of sand, silt, and clay to downgradient areas where they are deposited and further concentrated. It is important to note that the processes of major concentration of heavy minerals are due to flowing waters in rivers or streams and wind. In fluvial settings, slope provides an important factor for the concentration heavy mineral placers. In coastal settings, the actions of waves, currents, tides, and wind are forces that concentrate the heavy dense minerals, including the minerals of economic value.

The major thorium deposits in various parts of coastal Asia and South America are classified as sedimentary thorium deposits (Dill, 2010), which could also be described as thorium placers (Table 1). Both modern placer and paleoplacer deposits could cater to the world demand of thorium. Thorium-bearing minerals are widely known to accumulate in modern coastal placer deposits, with examples in India, Brazil, Sri Lanka, and Malaysia, to name a few (Fig. 1, Table 1). In India, shoreline-parallel concentrations of monazite in coastal sands in the States of Kerala, Tamil Nadu, and the recently discovered deposits in Orissa (Fig. 2; Mohanty et al., 2003a, b) have pushed India to the top level in production of thorium. These placer deposits resulted from fluvial drainage systems during the Quaternary. These monazite sands are of interest as a resource for economic recovery of the REEs, primarily cerium (Ce), obtained as a coproduct of titanium (Ti) oxide production in the form of ilmenite and rutile and zirconium (Zr) recovery from zircon.

Fig. 2.

Index map of southern India and northern Sri Lanka, showing locations of (1) historic and active heavy mineral sands operations discussed in this report, and (2) areas of Quaternary and Neogene sediments.

Fig. 2.

Index map of southern India and northern Sri Lanka, showing locations of (1) historic and active heavy mineral sands operations discussed in this report, and (2) areas of Quaternary and Neogene sediments.

Major Coastal and Fluvial Thorium (Monazite) Placer Deposits

Table 1.
Major Coastal and Fluvial Thorium (Monazite) Placer Deposits
Country State Placer district Latitude Longitude Comments References
Australia Western Australia Eneabba, Perth basin -29.79 115.30 About 2,5001 of monazite produced annually as a coproduct prior to 1995 Sheppard (1990);
Castor and Hedrick (2006)
Brazil Bahia Alcobaga -17.26 -39.22 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Espírito Santo Anchieta (Parati, Imbiri,Pipa de Viho, Maeba) -20.77 -40.57 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Espírito Santo Aracruz -19.95 -40.15 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Sergipe Brejo Grande - Pacatuba -10.43 -36.47 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Rio de Janeiro Buena (Buena Norte, Buena Sol) -21.52 -41.07 Active producer of monazite from beach placers Industrias Nucleares do Brasil SA (2013)
Brazil Rio Grande do Norte Camaratuba -6.89 -34.89 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Bahia Cumuruxatiba (Curumuxatiba, Comoxatiba) -18.31 -39.66 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Espírito Santo Guarapari (Praia do Vaz, Vila Velha, Rastinga, Canto do Riacho, Praia de Diogo) -20.70 -40.51 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Espírito Santo Itapemirim (Boa Vista, Siri) -21.17 -40.91 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Paraiba Mataraca -6.48 -34.97 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Bahia Porto Seguro district -16.43 -39.08 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Bahia Prado area -17.39 -39.21 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Rio de Janeiro Sao Joao de Barra (Barra Sao Joao) -21.40 -41.00 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Espírito Santo Serra (Jacareipe) -20.17 -40.19 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Bahia, Espirito Santo Vitoria -18.33 -39.66 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
China Guangxi Beihei 21.48 109.10 River and coastal placers; byproduct monazite Jackson and Christiansen (1993); Orris and Grauch (2002)
China Guangdong Dianbai 21.50 111.02 Coastal placers; by-product monazite Jackson and Christiansen (1993); Orris and Grauch (2002)
China Guangdong Haikang 20.98 110.07 River and coastal placers; by-product monazite Jackson and Christiansen (1993); Orris and Grauch (2002)
China Guangdong Nanshanhai 21.55 111.67 Coastal placers; by-product monazite Jackson and Christiansen (1993); Orris and Grauch (2002)
China Hainan Island Sai-Lao, Wuzhaung, and Xinglong districts 18.68 110.38 Coastal placers; by-product monazite Jackson and Christiansen (1993); Orris and Grauch (2002)
China Guangxi Xun Jiang 23.50 110.83 River placers; by-product monazite Jackson and Christiansen (1993); Orris and Grauch (2002)
India Orissa Erasama 20.15 86.51 Coastal placers containing monazite Mohanty et al. (2003a, b, 2004)
India Orissa Chhatrapur 19.34 85.01 Coastal placers containing monazite Mohanty et al. (2003a, b, 2004)
India Andhra Pradesh Visakhapatnam 17.66 83.27 Coastal placers containing monazite Raju et al. (2001)
India Kerala Manavalakurichi 8.14 77.30 Coastal placers containing monazite Tipper (1914); Raju et al. (2001)
India Kerala Chavara 8.99 76.52 Coastal placers containing monazite Prakash et al. (1991)
India Maharashtra Ratnagiri 17.02 73.28 Coastal placers containing monazite Raju et al. (2001)
Malaysia Selangor Batang Berjuntai 3.39 101.42 Fluvial tin placers; by-product monazite and xenotime Orris and Grauch (2002)
Sri Lanka Eastern Province Pulmoddai 8.95 80.99 Coastal placers containing monazite Lanka Mineral Sands Limited (2013)
Thailand Phang-nga Takua-Pa 8.87 98.35 Fluvial tin placers; by-product monazite and xenotime Economic and Social Commission for Asia and the Pacific (2001)
United States Idaho Central Idaho fluvial placers 44.42 -116.02 Fluvial placers; by-product monazite Staatz et al. (1980)
United States North Carolina and South Carolina Piedmont region fluvial placers 35.31 -81.54 5,0001 of monazite produced from 1887 to 1917 Overstreet et. al. (1968); Staatz et al. (1979)
United States Florida Mineral City 30.24 -81.39 About 11 of monazite produced in 1925 Staatz et al. (1980)
United States Florida Rutile Mining Co. mine 30.34 -81.60 Small amounts of monazite recovered from beach sands Staatz et al. (1980)
United States Florida Riz Mining Co. mine 27.64 -80.35 Dune sands; monazite as by-product from 1940s to 1955 Staatz et al. (1980)
United States Florida Green Cove Springs 29.87 -81.71 Beach deposits; monazite recovered as coproduct Staatz et al. (1980); Castor and Hedrick (2006)
United States Florida Boulogne 30.77 -81.98 Beach deposits; monazite recovered as coproduct Staatz et al. (1980)
Country State Placer district Latitude Longitude Comments References
Australia Western Australia Eneabba, Perth basin -29.79 115.30 About 2,5001 of monazite produced annually as a coproduct prior to 1995 Sheppard (1990);
Castor and Hedrick (2006)
Brazil Bahia Alcobaga -17.26 -39.22 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Espírito Santo Anchieta (Parati, Imbiri,Pipa de Viho, Maeba) -20.77 -40.57 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Espírito Santo Aracruz -19.95 -40.15 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Sergipe Brejo Grande - Pacatuba -10.43 -36.47 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Rio de Janeiro Buena (Buena Norte, Buena Sol) -21.52 -41.07 Active producer of monazite from beach placers Industrias Nucleares do Brasil SA (2013)
Brazil Rio Grande do Norte Camaratuba -6.89 -34.89 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Bahia Cumuruxatiba (Curumuxatiba, Comoxatiba) -18.31 -39.66 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Espírito Santo Guarapari (Praia do Vaz, Vila Velha, Rastinga, Canto do Riacho, Praia de Diogo) -20.70 -40.51 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Espírito Santo Itapemirim (Boa Vista, Siri) -21.17 -40.91 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Paraiba Mataraca -6.48 -34.97 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Bahia Porto Seguro district -16.43 -39.08 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Bahia Prado area -17.39 -39.21 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Rio de Janeiro Sao Joao de Barra (Barra Sao Joao) -21.40 -41.00 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Espírito Santo Serra (Jacareipe) -20.17 -40.19 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Bahia, Espirito Santo Vitoria -18.33 -39.66 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
China Guangxi Beihei 21.48 109.10 River and coastal placers; byproduct monazite Jackson and Christiansen (1993); Orris and Grauch (2002)
China Guangdong Dianbai 21.50 111.02 Coastal placers; by-product monazite Jackson and Christiansen (1993); Orris and Grauch (2002)
China Guangdong Haikang 20.98 110.07 River and coastal placers; by-product monazite Jackson and Christiansen (1993); Orris and Grauch (2002)
China Guangdong Nanshanhai 21.55 111.67 Coastal placers; by-product monazite Jackson and Christiansen (1993); Orris and Grauch (2002)
China Hainan Island Sai-Lao, Wuzhaung, and Xinglong districts 18.68 110.38 Coastal placers; by-product monazite Jackson and Christiansen (1993); Orris and Grauch (2002)
China Guangxi Xun Jiang 23.50 110.83 River placers; by-product monazite Jackson and Christiansen (1993); Orris and Grauch (2002)
India Orissa Erasama 20.15 86.51 Coastal placers containing monazite Mohanty et al. (2003a, b, 2004)
India Orissa Chhatrapur 19.34 85.01 Coastal placers containing monazite Mohanty et al. (2003a, b, 2004)
India Andhra Pradesh Visakhapatnam 17.66 83.27 Coastal placers containing monazite Raju et al. (2001)
India Kerala Manavalakurichi 8.14 77.30 Coastal placers containing monazite Tipper (1914); Raju et al. (2001)
India Kerala Chavara 8.99 76.52 Coastal placers containing monazite Prakash et al. (1991)
India Maharashtra Ratnagiri 17.02 73.28 Coastal placers containing monazite Raju et al. (2001)
Malaysia Selangor Batang Berjuntai 3.39 101.42 Fluvial tin placers; by-product monazite and xenotime Orris and Grauch (2002)
Sri Lanka Eastern Province Pulmoddai 8.95 80.99 Coastal placers containing monazite Lanka Mineral Sands Limited (2013)
Thailand Phang-nga Takua-Pa 8.87 98.35 Fluvial tin placers; by-product monazite and xenotime Economic and Social Commission for Asia and the Pacific (2001)
United States Idaho Central Idaho fluvial placers 44.42 -116.02 Fluvial placers; by-product monazite Staatz et al. (1980)
United States North Carolina and South Carolina Piedmont region fluvial placers 35.31 -81.54 5,0001 of monazite produced from 1887 to 1917 Overstreet et. al. (1968); Staatz et al. (1979)
United States Florida Mineral City 30.24 -81.39 About 11 of monazite produced in 1925 Staatz et al. (1980)
United States Florida Rutile Mining Co. mine 30.34 -81.60 Small amounts of monazite recovered from beach sands Staatz et al. (1980)
United States Florida Riz Mining Co. mine 27.64 -80.35 Dune sands; monazite as by-product from 1940s to 1955 Staatz et al. (1980)
United States Florida Green Cove Springs 29.87 -81.71 Beach deposits; monazite recovered as coproduct Staatz et al. (1980); Castor and Hedrick (2006)
United States Florida Boulogne 30.77 -81.98 Beach deposits; monazite recovered as coproduct Staatz et al. (1980)

Classification of Placer Deposits

Based on their mode of transportation and the site of deposition, placers are classified as (1) eluvial, (2) alluvial or fluvial, (3) eolian, (4) beach, and (5) fossil placers.

  1. Eluvial placers are formed upon the release of minerals from the rock matrix, caused by the decomposition of rock in place from weathered deposits primarily due to precipitation and aeolian activity. This is the embryonic stage in the development of placers (Gupta, 2003). Notable Indian examples are the cassiterite, columbite, and tantalite placer deposits in the Bastar district in the state of Madhya Pradesh in central India (Fig. 2; Suryanarayan et al., 1979).

  2. Alluvial placers represent the next stage in the placer formation. The heavy minerals are introduced into the fluvial system by the action of runoff, gravity, and/or by the erosive action of the stream itself. Renowned examples are the gold-bearing alluvial placer deposits that fed the famous California (United States) gold rush in the 19th century. Economic examples of xenotime-bearing fluvial placer deposits occur in India (Rai et al., 1991), Malaysia (Castor and Hedrick, 2006), and Thailand (Economic and Social Commission for Asia and the Pacific, 2001, p. 72-74).

  3. Eolian deposits, formed by the actions of winds, can hold concentrations of heavy minerals. These types of deposits occur in arid/semiarid regions, where the influence of wind is strong and sufficient vegetation does not exist to cover the soil. Wind action progressively concentrates the heavy minerals by blowing away the associated light minerals over time (Nikiforova et al., 2005, 2007). Prominent examples are eolian gold deposits of Australia. The Teri deposits of Tamil Nadu (Fig. 2) are aeolian in origin. The Trail Ridge deposit of north-central Florida is a Pliocene-age complex of aeolian sands, from which DuPont produces titanium minerals, zircon, and staurolite (Dupont, 2014). The sand dunes of the Richards Bay area (Richards Bay Minerals, 2013) on the east coast of South Africa have been a highly productive source of zircon, rutile, and ilmenite.

  4. Beach placers are formed by the interaction of terrestrial processess with coastal hydrodynamics. The heavy minerals are carried in sediments, transported to the coastal area by various processes of detrital transport, then selectively panned, sorted and deposited at suitable locations by the action of waves and currents. The factors controlling the formation of beach placers are complex and include geomorphology of the area, climate, drainage pattern, coastal processes, and neotectonics. The heavy minerals are concentrated by a combination of these processes in the upper part of the beach, where the actions of the wind may erode them and form heavy mineral-rich coastal dune deposits (deposit type 3 above; Kudrass, 2000). Most of the important deposits of ilmenite, rutile, zircon, monazite, and garnet occur in the form of beach placers. India has some of the world’s largest placer deposits along its long southeast and southwest coastlines.

  5. Fossil (paleo) placers formed in the geologic past due to processes similar to modern deposits. Fossil placers become exposed by factors such as climate change and/ orepirogenic movements and eustasy. Along the coasts of India and adjoining areas of Sri Lanka (Singhvi et al., 1986) there are considerable reserves of fossil placers known to exist (Ali et al., 2001); these deposits formed during previous low stands of sea level. Other examples of fossil placers are discussed in this article. Fossil placers can be reworked by erosion and act as sources of recent deposits.

Fig. 3.

Index map of Australia showing the Cenozoic sedimentary basins and other districts (red dots; Tiwi Islands, Cape York, North Stradbroke Island) that host deposits of heavy mineral sands that are currently being mined.

Fig. 3.

Index map of Australia showing the Cenozoic sedimentary basins and other districts (red dots; Tiwi Islands, Cape York, North Stradbroke Island) that host deposits of heavy mineral sands that are currently being mined.

Examples of Monazite-Bearing Placer Districts

By-product monazite has been recovered in the past from placer deposits in Australia, Brazil, India, Malaysia, Thailand, China, New Zealand, Sri Lanka, Indonesia, Zaire, Korea, and the United States. Until the mid-1960s, with the advent of full rare earth production from the Mountain Pass carbonatite deposit in southeastern California, monazite placers were the world’s principal source of REE production (Tse, 2011, Fig. 1). Monazite has recently been recovered from beach and alluvial placers in India, Malaysia, Sri Lanka, Thailand, and Brazil (Table 1). Indian beach placers are the principal source for ongoing production of monazite and for this reason the Indian deposits are described in more detail as examples of this deposit type.

Heavy mineral sands deposits (placers) occur on every continent, likely including Antarctica. The REE deposit dataset of Orris and Grauch (2002) lists 369 REE-bearing placer deposits and occurrences, including 264 shoreline placers, 78 alluvial placers, 13 paleoplacers, and 14 unclassified placers. The examples of monazite-bearing placers that follow should not be regarded as a complete listing of all known occurrences of this deposit type throughout the world. Rather, the deposits described here are examples of significant deposits of monazite-rich, heavy mineral sands that have been worked in the past or are being mined at this time.

Australia

The vast majority of the heavy mineral and associated monazite resources of Australia are hosted by ancient beach and sand dune deposits that formed along middle Eocene to Pleistocene strandlines (Hoatson et al., 2011). Significant fossil beach deposits of heavy minerals occur in three inland Cenozoic-age sedimentary basins of western and southern Australia, which are the Canning, Perth, Murray, and Eucla basins (Fig. 3). In the northeastern part of the Canning basin in the northeastern part of Western Australia, heavy mineral sands are currently (2014) mined inland of the coast near Derby. The Perth basin, in the southwestern part of Western Australia, hosts substantial deposits of heavy minerals within Cenozoic strandline strata that parallel the coast north and south of Perth. The heavy mineral beach deposits of the Murray basin occur in Cenozoic paleostrandlines in New South Wales, Victoria, and South Australia. The Eucla basin bounds the coast of the southwestern part of South Australia and southeastern part of Western Australia.

Heavy mineral-rich beach and dune sand deposits in the Perth basin of Western Australia have been extensively mined since the 1970s. The sands were deposited along strandlines from the Pliocene to early Pleistocene. The Eneabba mining district in the northern part of the Perth basin (north of Perth, Fig. 3) has been a substantial producer of heavy minerals, principally rutile, zircon, and ilmenite, as well as a former producer of monazite as a coproduct. Reportedly, prior to 1995 about 2,500 t of monazite were recovered annually as a coproduct of titanium minerals and zircon processing in the Eneabba district (Castor and Hedrick, 2006; Hoatson et al., 2011). Production of monazite in the district peaked between 1975 and 1985 (Shepherd, 1990). The source of the monazite in the ancient dune and beach sands of the Eneabba district are thought to be underlying Mesozoic sedimentary rocks, with Archean crystalline rocks of the basement being the original source (Shepherd, 1990). In the Eneabba deposits, monazite concentrations can be as much as 7% near the southern end of the barrier complex, deposited in the direction of the longshore drift near a relic headland (Shepherd, 1990). On average, heavy minerals compose about 6% of the paleoshore sands mined in this district, with monazite composing 0.5 to 7.0% of this heavy mineral suite (Shepherd, 1990). Heavy mineral production remains active today in the district, but monazite is not currently recovered as a product and is returned to the mined site. As an example of recent heavy mineral production capacity, in 2010 Iluka Resources reported a mining and processing output from their Perth basin operations of 41,500 t of rutile, 347,500 t of synthetic rutile, 255,800 t of ilmenite, and 46,200 t of zircon (Geoscience Australia, 2012).

Within the Murray basin, near Horsham in the Wimmera region of western Victoria, the WIM150 mineral sands deposit (Fig. 3) reportedly contains substantial resources of monazite and xenotime, associated with titanium minerals and zircon in the heavy mineral suite. The deposit is about 14 m thick, comprises titanium-zircon-rich sand bodies formed along a late Tertiary strandline. The mineral sands project here is in an advanced stage of premining development and permitting, with plans to recover the titanium minerals and zircon. It appears that the associated monazite and xenotime will not be exploited in the foreseeable future of this project; however, the deposit reportedly contains more than 580,000 t of monazite and 170,000 t of xenotime (O’Driscoll, 1988).

Roy and Whitehouse (2003) attributed the high concentrations of heavy minerals in strandline sands in the Murray basin to barrier sand complexes, totaling 400 km in length, which formed during Pliocene seashore progradation driven by sealevel oscillations. They suggest that the heavy minerals in the sand deposits were derived from storm and wave reworking of underlying heavy mineral-bearing Miocene sands, and that erosion and deposition were aided by growth faults.

Brazil

The monazite placers of the Brazilian coast include elevated paleobeaches, modern beaches, sand dunes, and the banks, channels, and bars of streams that deposit sediments near the shore. Cretaceous and Tertiary sandstones that formed along paleostrandlines crop out near the modern beach; some sandstone intervals are rich in monazite, ilmenite, and zircon. These sandstones are eroded and disaggregated by high-tide waves and storm surges. These processes redeposit sand and heavy minerals into the surf zone, where the heavy minerals are again reworked and sorted by waves, longshore drift, and tides. Thus, the Cretaceous-Tertiary strandline deposits, which occur in slightly higher outcrops near the modern beach, are another source (often richer source) of monazite. According to the study of Leonardos (1974), the principal inland sources of detrital monazite along the central Brazilian coast are Archean amphibolite-granulite rocks and Cretaceous and Tertiary sedimentary rocks derived from erosion of these Archean rocks.

More than a dozen mined monazite-bearing placer districts occur intermittently along the central coast of Brazil (Overstreet, 1967; Orris and Grauch, 2002). Coastal placers that were past producers of monazite occur scattered along the coast between the city of Campos in the state of Rio de Janeiro on the southern end to the southernmost area of the coast in the state of Rio Grande do Norte on the north end (Fig. 4). Monazite was recovered as a coproduct of the more profitable titanium minerals (ilmenite, rutile) and zircon. In contrast to most heavy mineral sands operations, many of the Brazilian deposits were mined primarily for their monazite, sought foremost as a source of thorium. According to Overstreet (1967), from 1900 to 1947 Brazil exported 62,115 short tons (56,350 t) of monazite concentrate, with the monazite recovered from beach placers. Since the early 1990s, the Buena placer district (Fig. 4), which includes the Buena Norte and Buena Sol deposits, has been the only active Brazilian producer of monazite through a state-administered program (Indústrias Nucleares do Brasil SA (INB), 2013).

The coastal sand deposits of Brazil have some of the highest monazite concentrations known in the world, with as much as 8% average monazite content in some sand bodies (Overstreet, 1967). The Guarapari coastline of Espiroto Santo, near Campos (Fig. 4), is a popular tourist destination known for its white sand beaches, but this shoreline is also known for its very high level of background radioactivity due to abundant monazite. In this area, the recently and historically mined Buena Norte deposit has a reported monazite content of 0.83% (Jackson and Christiansen, 1993). Analyses of Brazilian monazites suggest that their average REE oxide content is typically around 57 to 60%, with preferential enrichment in the light REEs (Overstreet, 1967; Orris and Grauch, 2002).

Summarizing the monazite endowment in Brazil’s coastal deposits state-by-state, Hedrick (1997, p. 61.4) reported the following “measured reserves” of monazite (more properly stated, “measured resources”): “Measured reserves were 16,622 tons [metric tons] grading 53.88% REOs in Bahia, 29,210 tons grading 57% REOs in Ceara, 697,382 tons grading 60% REOs in Espirito Santo, 326,766 tons grading 59.72% REOs in Minas Gerais, and 17,166 tons grading 60% REOs in the state of Rio De Janeiro.” Most of these monazite resources remain. The proximity of many of these mineralrich beach deposits to resorts and other population centers has been a major factor in restricting their development.

China

China has considerable resources of monazite within placer deposits; however, scant information on the characteristics and production of these resources has been published. Jackson and Christiansen (1993) reported that China produced 10,200 t REOs from placer deposits in 1989. Since that time, rare earth production from placer deposits in China is unavailable.

Some of the productive monazite-bearing placer districts in China (Jackson and Christiansen, 1993; Orris and Grauch, 2002) are as follows:

  1. Beihei district, located near 21° 29’ N, 109° 06’ E in the Guangxi province. A mixture of river and marine placers along the coast, containing about 1.5% heavy minerals comprised of ilmenite, rutile, zircon, and monazite. A producer of by-product monazite.

  2. Dianbai district, located near 21° 30’ N, 111° 01’ E in the Guangdong province. Placers on the coast, containing about 2.3% heavy minerals comprise ilmenite, rutile, zircon, and monazite. A producer of by-product monazite.

  3. Haikang district, located near 20° 56’ N, 110° 04’ E in the Guangdong province. A mixture of river and marine placers that contain ilmenite, zircon, rutile, monazite, and xenotime. A producer of by-product monazite.

  4. Nanshanhai district, located near 21° 32’ 45” N, 111° 40’ 00” E in the Guangdong province. Coastal placers that contain ilmenite, zircon, rutile, monazite, and xenotime. A producer of by-product monazite.

  5. Sai-Lao, Wuzhaung, and Xinglong placer districts, all located on Hainan Island (see Orris and Grauch, 2002). These placers contain ilmenite, zircon, anatase, cassiterite, monazite, magnetite, and chromite. Producers of by-product monazite.

  6. Xun Jiang district, located near 23° 30’ N, 110° 50’ E in the Guangxi province. River deposits containing 6.0% heavy minerals comprise ilmenite, rutile, zircon, and monazite.

India

The history of placer deposits as a source of economic minerals began with the discovery of monazite in the beach sands of Manavalakurichi (Tipper, 1914) in southernmost India (Fig. 2). The beach sands were first worked in 1911 and subsequently were rapidly developed with the establishment of the TiO2 (titania) pigment industry in Europe and America. However, by the 1950s ilmenite production saw a sudden decrease in India. This was in part due to the discoveries of new deposits in Australia and Canada, compounded by the presence of undesirable impurities, such as chromium and ferric iron, in Indian ilmenite. However, after nationalization of all the major deposits in India, the national production of ilmenite and rutile has increased over the years. The current production rate is about 140,000 t of ilmenite and 6,000 t of rutile. Governmental concerns, such as the Indian Rare Earths Ltd. and Kerala Minerals and Metals Ltd., are involved in the production and marketing of the placer minerals.

Fig. 4.

Index map showing monazite-producing placer deposits (red squares) along the central coastline of Brazil. The active monazite producer is the Buena district (Industrias Nucleares do Brasil SA (INB), 2013), the southernmost placer district shown in the map.

Fig. 4.

Index map showing monazite-producing placer deposits (red squares) along the central coastline of Brazil. The active monazite producer is the Buena district (Industrias Nucleares do Brasil SA (INB), 2013), the southernmost placer district shown in the map.

Over the last few decades new deposits have been discovered in coastal placers of India, such as Chhatrapur in Orissa and Visakhapatnam in Andhra Pradesh along the east coast, and Ratnagiri in Maharashtra on the west coast of the country (Fig. 2). Along the coastal stretches of Tamil Nadu, deposits of heavy minerals occur in the inland areas in the form of teri sands, also known as red sands in Tamil Nadu (Babu et al., 2009). The current reserves of the placer minerals in India are as follows: 278 Mt ilmenite, 13.49 Mt rutile, 18 Mt zircon, 7 Mt monazite, 84 Mt sillimanite, and 86 Mt garnet (Raju et al., 2001).

The major placer concentrations of India are located along the east and west coasts (Fig. 2). For example, detrital monazite occurs in ilmenite-bearing heavy mineral sands of Chavara and Manavalakurichi, as well as less extensive detrital monazite deposits in parts of coastal Orissa, Andhra Pradesh, and Tamil Nadu. Thus, the Eastern Ghats group of rocks have been more widely spread, though as localized deposits, in comparison to sediments derived from the Western Ghats group, which is mostly concentrated in Kerala. Apart from these coastal placers, there are numerous inland placers in Maharashtra. These deposits generally occur in stream segments with low current velocity, such as point bar deposits, within ripple marks, around submerged bars, or in narrow zones at the bottom of a stream.

The heavy mineral content of beach placers along the southern coast of Orissa primarily depends on the nature of the hinterland rocks present in the region. The source rocks are dominated by granulite facies of khondalites, charnockites, and leptynolites (Mohanty et al., 2003b), plus the presence of granite intrusions, pegmatites, quartz veins, and metasediments. Based on the thorium oxide concentration in the monazite sands, it was inferred that the monazite grains were derived primarily from the granulite-facies metamorphic rocks belonging to the Eastern Ghats group of rocks (Mohanty et al., 2003b). Radioactive elements thorium (Th) and uranium (U) and rare earth elements (lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), and samarium (Sm)) are highly enriched in the monazite sands of coastal Orissa. Ilmenites are the major heavy minerals and constituite about 65 to 80% of the total heavy mineral assemblage (Mohanty et al., 2003b). Earlier studies (Mohanty et al., 2003a) suggest that the ilmenite grains are derived from higher grade (granulite-facies) metamorphic rocks. The important feature observed commonly in the monazites is the abundance of total REE as compared to the actinides; additionally, the monazites are enriched in La, Ce and Nd. The greater content of yttrium oxide (Y2O3) has been attributed to the garnet-free paragenesis (Mohanty et al., 2003a).

In extensive studies undertaken along peninsular India, especially along the eastern and western coasts, in addition to the marine regressions and transgressions during the Quartenary the rivers also play a significant role in beach placer development (Prakash et al., 1991; Mohanty et al., 2004; Sengupta et al., 2005). Three factors responsible for placer mineralization, especially the radioactive minerals, are (1) their distribution in the hinterland rocks, (2) geologic controls due to presence of rivers attributed to its morphology, and (3) structures that control the drainage patterns (Sinha-Roy, 1982). This implies the significant role of weathering and transport in the formation of heavy mineral placers. This relationship is true for not only the placer mineralization along the Western Ghats group of rocks, especially the southern coast of Kerala, such as the Chavara placer deposit, but also in the Eastern Ghats (Prakash et al., 1991). The latter comprises rich placer deposits along the southern Orissa coast, such as the Erasama (Fig. 5) and Chhatrapur deposits (Fig. 6). The southern rivers in Kerala, India, for example, the Neyyar, Karamana, and Vamanapuram Rivers, carry enhanced concentrations of heavy minerals (that include radioactive minerals) into the pensisular region, aided by the southwestern monsoon (Prakash et al., 1991). In Tamil Nadu, extensive studies of zircons in placer deposits located along the southern coast show the zircons are enriched in REEs, especially europium (Eu) and (Ce); this indicates that the bedrock source for the zircons was primarily charnockites (Angusamy et al., 2004). In a similar manner, the role of Rushikulya River, in the Ganjam district, southern coast of Orissa (Fig. 7), aided in the formation of the rich placer deposits sourced from the Eastern Ghats group of rocks for Chhatrapur placers. Additionally, high-grade metasedimentary rocks along the hinterland, transported by the Mahanadi River drainage basin, formed the Erasama placer deposit (Mohanty et al., 2004; Sengupta et al., 2005). For the Eastern Ghats group of rocks, it has been observed that charckonites and the khondalites are primarly responsible for the enhanced concentration of thorium as compared to uranium. Along the Eastern Ghats there are major and notable heavy mineral placers, located in the States of Tamil Nadu, Andhra Pradesh, and Orissa, respectively (Ali et al., 2001; Mohanty et al., 2003b). Recent studies indicate that the Eastern Ghats group is the major source for the heavy mineral assemblage observed in the placer deposits (Raju et al., 2001). The heavy mineral placers both in the eastern and western part of India are highly enriched in thorium (Mohanty et al., 2003a, b, 2004; Sengupta et al., 2005).

Malaysia

Prior to the domination of global yttrium production by China in the late 1980s, xenotime-bearing alluvial placer deposits in Malaysia were the largest sources of yttrium in the world (Castor and Hedrick, 2006). The sources within Malaysia are alluvial tin placer deposits, which carry considerable cassiterite accompanied by ilmenite, monazite, and xenotime. Recently, tailings produced from past tin placer mining have been reprocessed to recover monazite and xenotime. In this manner, 350 t REOs were produced from Malaysia in 2012 (Gambogi, 2013).

Sri Lanka

Modern beach deposits on the northeastern coast of Sri Lanka have some of the highest concentrations of heavy minerals in the world. Beach sands of this region are mined and processed by Lanka Minerals Sands Ltd. (2013), a company owned by the Government of Sri Lanka, and the successor to Ceylon Mineral Sands Corp. The company’s primary mining operations and processing plants are located just east of Pulmoddai on the northeast coast of Sri Lanka (Fig. 2). Products from the beach sands are ilmenite, rutile, and zircon; sillimanite, monazite and garnet also exist, with monazite reportedly composing 0.3% of the heavy mineral fraction (Herath, 1990). According to the company, in some stretches of beach the heavy minerals can compose as much as 90% of the sand deposits; ilmenite forms 65% of the heavies, rutile forms 10%, and zircon forms 10% (Lanka Minerals Sands Ltd., 2013). Heavy mineral-rich beach sands extend along the shore about 8 km south from Kokkilai Lagoon (Fig. 2) and they extend inland from the ocean for about 370 m. The stretch of beach that extends about 40 km north and south of Pulmoddai in northeastern Sri Lanka represents one of the richest deposits of heavy mineral sands in the world (Lanka Minerals Sands Ltd., 2013).

Fig. 5.

Map showing the sample locations in the Erasama beach placer deposit, Orissa, India (after Mohanty et al., 2004).

Fig. 5.

Map showing the sample locations in the Erasama beach placer deposit, Orissa, India (after Mohanty et al., 2004).

Fig. 6.

Map showing sample locations in the Chhatrapur beach placer deposit, Orissa, India (after Mohanty et al., 2004).

Fig. 6.

Map showing sample locations in the Chhatrapur beach placer deposit, Orissa, India (after Mohanty et al., 2004).

Fig. 7.

Index map of the Rushikulya beach placer deposit along the Orissa coast, southeast India, showing sample locations (after Sulekha Roa et al., 2009).

Fig. 7.

Index map of the Rushikulya beach placer deposit along the Orissa coast, southeast India, showing sample locations (after Sulekha Roa et al., 2009).

Fig. 8.

Map of monazite-bearing alluvial placers in North and South Carolina, United States. Modified from Staatz et al. (1979).

Fig. 8.

Map of monazite-bearing alluvial placers in North and South Carolina, United States. Modified from Staatz et al. (1979).

Monazite-bearing alluvium in southwestern Sri Lanka, specifically stream sediments of the Bentota River, have been described as “one of the world’s most thorium rich sediments” (Rupasinghe et al., 1983, p. 1). Monazite is carried by this river system into seasonal beach sand deposits at Kaikawala and Beruwala. Monazite was once mined on a small scale at Kaikawala beach. Analyses of these monazites by Rupasinghe et al. (1983) found them to be highly enriched in the light REEs relative to the heavy REEs, with a negative Eu anomaly when normalized to chondrite values (Rupasinghe and Dissanayake, 1984).

Thailand

Tin (in cassiterite) has been mined from alluvial placers in Thailand for over 1,000 years, but much more recently they initiated by-product recovery of monazite (starting in 1969), ilmenite (in 1976), and xenotime (in 1977; Economic and Social Commission for Asia and the Pacific, 2001, p. 72-74). Production of REOs from Thailand decreased steadily from the 1980s to 1995, which was their last year of significant monazite and xenotime production. Similar to the Malaysian rare-earth resources, in Thailand the monazite and xenotime are recovered as by-products from the retreatment of earlier processing plant tailings derived from tin placers. The host tin placers, those enriched in monazite and xenotime, are alluvial deposits that were mined by gravel pump; these deposits occur mainly in southern Thailand (shown in Economic and Social Commission for Asia and the Pacific, 2001, p. 72-74).

United States

Monazite-bearing, heavy mineral placers of both alluvial and coastal origins are well known in the United States. Some of these placers produced modest tonnages of monazite in the past. A century ago, monazite was produced from alluvial placers in mountain valleys of North Carolina and South Carolina, and during the 1950s monazite was recovered from stream alluvium in mountain valleys of central Idaho. As recently as 1994, heavy mineral sands deposits in Florida, which formed along Pliocene and Pleistocene strandlines, were worked for titanium minerals and zircon but also produced monazite as a coproduct. As of 2014, monazite is not recovered at an active placer operation in the United States.

Monazite-brearing alluvial placers in North and South Carolina: In 1887, a few short tons of monazite were produced from stream deposits in the Piedmont region of North and South Carolina, giving this region the distinction of being the world’s first supplier of thorium (Olson and Overstreet, 1964). Monazite-bearing placers of this region were worked by small-scale sluice operations from 1887 to 1911 and 1915 to 1917, producing a total of about 5,000 t of monazite (Overstreet et al., 1968). Monazite mining ended here in 1917, not because reserves had been exhausted, but rather because the beach deposits of India and Brazil were producing thorium at lower cost.

The high-grade monazite placers of the Piedmont of North and South Carolina occur between the Catawba River in the northeast and the Savannah River in the southwest (Fig. 8). The stream-sediment deposits across this region are generally consistent in character; the heavy mineral concentrations are greatest in the headwaters areas. Stacked layers of unconsolidated sediments of gravel, sand, clay, and clayey silt form an average total thickness of about 4.5 m (15 ft; Staatz et al., 1979). Monazite typically occurs in all units, but is generally most abundant in the basal gravel layers and least abundant in the clay layers. Dredging in this region between the summers of 1955 and 1958 (Williams, 1967) found heavy mineral contents of about 1 to 1.5%, with monazite forming about 8% of this fraction (Mertie, 1975). Overall, these dredging operations recovered monazite, ilmenite, rutile, zircon, and staurolite (Williams, 1967).

According to Staatz et al. (1979), the heavy mineral content of the placer deposits of the Piedmont region ranges from 0.15 to 2.0%, with monazite forming about 3.5 to 13% of the heavy minerals. Other parts of the heavy mineral fraction include ilmenite, 20 to 70%; garnet, 2 to 50%; rutile, 0.3 to 7%; zircon, trace to 14%; and sillimanite and kyanite together, trace to 20%. In some Piedmont placer deposits, additional heavy minerals include epidote, magnetite, xenotime, tourmaline, sphene, staurolite, andalusite, and an unidentified black radioactive mineral (Staatz et al., 1979). Analysis of 52 samples of alluvial monazite from this region (Mertie, 1975) found that the monazite contains 60 to 63% total REE oxides and 2.5 to 7.8% Th oxide content, with a mean value of 5.67% Th.

The Piedmont region of the southeastern United States is underlain by crystalline, high-grade metamorphic rocks intruded by quartz monzonite and pegmatite. The monzonite and pegmatite intrusions vary from monazite-bearing to monazite-free. Overstreet (1967) suggested that the primary source of the alluvial monazite was the high-grade metamorphic rocks, particularly sillimanite schist.

Monazite alluvial placers in Idaho: At least 11 monazitebearing placer districts exist in the valleys of a region extending north of Boise, Idaho, and along the western flank of the Idaho batholith (Fig. 9). Monazite was first recognized here in 1896, as the heavy, yellow to brownish-yellow mineral that collected with other heavy minerals and gold within the sluice boxes of gold placer operations in the Boise basin near Idaho City, Centerville, and Placerville (Lindgren, 1897). In 1909, a mill designed to capture the monazite was built by the Centerville Mining and Milling Co. Only a small amount of monazite concentrate was produced for its Th content before the mill burned down in a forest fire in 1910.

In the 1950s, two areas of west-central Idaho were mined by dredges for monazite recovery—Long Valley and Bear Valley (Fig. 9). Beginning in September 1950, Long Valley was worked by three dredges that were earlier used to recover gold but later converted to recover monazite. The dredges were redesigned for monazite recovery with assistance from the U.S. Bureau of Mines under the sponsorship of the U.S. Atomic Energy Commission. The history of these dredging operations is described by Argall (1954) and Staatz et al. (1980, p. 9-16, and references cited therein). The heavy minerals recovered in the Long Valley district were dominated by ilmenite (84% of heavies), followed by monazite (8%), garnet (5%), and zircon (3%). During this five-year period, Staatz et al. (1980) estimated that the three dredges recovered 6,430 t of monazite. The dredging ended here in mid-1955, when the government stockpile order was fulfilled.

Rare earth elements and thorium were also unintentionally recovered within the minerals euxenite and monazite from the Bear Valley placers. The Bear Valley placers were worked by first one dredge in 1955, then a second in 1956, with the intent to recover niobium (Nb) and tantalum (Ta) for another federal government contract. According to Staatz et al. (1980, p. 10), “from alluvium of Bear Valley, 2,049 short tons [1,858 metric tons] of euxenite, 83.5 tons [75.7 metric tons] of columbite, and 54,862 tons [49,760 metric tons] of ilmenite were recovered.” No records of the monazite recovery were kept.

The U.S. Geological Survey (Staatz et al., 1980) determined that the five most important monazite districts in Idaho are Long Valley, Bear Valley, the Boise basin, the Burgdorf Warren area, and the Elk City-Newsome area (Fig. 9). The reported thorium oxide contents of monazite in the Idaho placer deposits range from 2.2 to 6.24%. Only a few analyses for REE were conducted on monazites from Idaho placers, which indicated these monazites contain 63% total REE oxides. Staatz et al. (1980) calculated thorium reserves for each of the five major placer districts individually, indicating the five districts have total reserves of about 9,130 t of Th oxide. The REE resources of the five placer districts would presumably be at least 10 times the Th resource, because the typical monazite contains about 63% total REE oxides and 2.2 to 6.24% Th oxide.

The primary source of the resistant REE-thorium-bearing minerals in the Idaho placers is thought to be the Idaho batholith, in particular the quartz monzonite and pegmatite phases of the batholith (Mackin and Schmidt, 1957). The most common heavy minerals in the alluvial deposits (in generally decreasing amounts) are ilmenite, magnetite, sphene, garnet, monazite, euxenite, zircon, and uranothorite (uranium-rich thorite).

Monazite-bearing coastal sands in northeastern Florida: Modern beach sands near Mineral City (now known as Ponte Vedra) were mined chiefly for ilmenite from 1916 to 1929 (Staatz et al., 1980), about 1 km west of the ocean and just east of Jacksonville. Reportedly one short ton (0.9 t) of monazite was produced in 1925 (Staatz et al., 1980).

From 1943 to 1968, the Rutile Mining Co. recovered ilmenite, rutile, zircon, and small amounts of monazite from Pleistocene and Pliocene beach sands just east of Jacksonville.

The Riz Mineral Co. mined dune sands near Vero Beach from the early 1940s until 1955, recovering ilmenite, rutile, zircon, and monazite (Staatz et al., 1980).

A variety of companies mined and processed Pleistocene beach deposits at Green Cove Springs to recover their heavy minerals, particularly titanium minerals and zircons (the Duval Upland ridge deposit); these deposits are located south of Jacksonville and west of St. Johns River. Reportedly, about 500 t of monazite per year were recovered as a coproduct from the Green Cove Springs deposits (Castor and Hedrick, 2006). Recently, Iluka Resources resumed mining from this deposit to recover titanium minerals and zircon; they ended their mining activities there in 2005 and the site is now being reclaimed by the company. The deposits at Green Cove Springs contained an average of 3% heavy minerals, which included ilmenite, leucoxene, rutile, zircon, and monazite (Staatz et al., 1980).

From 1974 to 1978, Humphrey Minerals mined a Pleistocene beach deposit near Boulogne in northeastern Florida. This ore body averaged about 4% heavy minerals; titanium minerals, zircon, and monazite were recovered. Reportedly, monazite composes 0.3 to 0.4% of the heavy mineral assemblage in this deposit (Staatz et al., 1980). This Pleistocene shoreline facies extends to the north into Georgia, where this unit was earlier mined by the same company at nearby Folkston, Georgia.

Industrial Mineral Commodities in Heavy Mineral Placers

Placer deposits are the main source of titanium feedstock for the titanium dioxide (TiO2) pigments industry (Murphy and Frick, 2006), through recovery of the minerals ilmenite (Fe2+TiO3), rutile (TiO2), and leucoxene (an alteration product of ilmenite). Heavy mineral sands (placers) are also the principal source of zircon (ZrSiO4), which is often recovered as a coproduct. Other heavy minerals produced as coproducts from some deposits are sillimanite/kyanite, staurolite, monazite, and garnet.

Prior to full-scale mining and production from the Mountain Pass carbonatite deposit, California, in the mid-1960s, alluvial placers were the primary source of rare-earth elements for the world. Today, deposits of monazite [(Ce,La,Nd,Th)PO4], mainly in beach placers, are again sought as a source of rare earth elements as well as thorium, most particularly at several coastal sand deposits in southern India. The processed Th is to be used in Th-based nuclear power under development in India and elsewhere.

Fig. 9.

Generalized map of known monazite-bearing alluvial placer districts in Idaho. Modified from Staatz et al. (1980).

Fig. 9.

Generalized map of known monazite-bearing alluvial placer districts in Idaho. Modified from Staatz et al. (1980).

Ore and Gangue Mineralogy

Heavy mineral-rich placer deposits encompass a wide range of minerals with varying values of specific gravity. They have been generally classified (Emery and Noakes, 1968) as placers that contain: (1) “very heavy” minerals with specific gravity between 6.8 and 21, such as cassiterite and native gold; (2) “light” heavy minerals with specific gravity between 4.2 and 5.3, such as ilmenite, rutile, monazite, xenotime, and zircon; and (3) minerals with densities between 2.9 and 4.1, such as garnet, sillimanite, and hypersthene. Folk (1980) divided the heavy minerals into four groups, based on their physical and chemical nature—opaques, micas, ultrastables, and metastables.

The economic heavy minerals in placer deposits are especially durable and resistant to chemical breakdown, and thus survive the torturous journey from the bedrock source area to the site of deposition, as distant as the coast or the sea (offshore deposition). The suite of heavy minerals most commonly includes Ti-bearing minerals (ilmenite, rutile, and leucoxene) and zircon, and can also contain sillimanite/kyanite, staurolite, monazite, garnets, xenotime, and others. In the vast majority of economic heavy mineral coastal deposits (“heavy mineral sands”), ilmenite is the most abundant heavy mineral and the principal ore mineral, followed by rutile, leucoxene (“altered ilmenite”), and zircon. Together, ilmenite, rutile, and zircon often compose more than 80% of the heavy mineral suite. Other heavy minerals that are sometimes recovered as economic coproducts include garnets, sillimanite, staurolite, cassiterite (“tin placers”), monazite, and xenotime. Economic deposits can contain less than 1% heavy mineral content, but composite grades are usually more than 2% and locally can exceed 10%. The economic viability of a heavy mineral sand deposit is dependent on the interplay of many factors, such as its location, depth, size, heavy mineral grade and mineralogy, and market prices.

Resources of REEs in placer deposits occur principally in monazite [(Ce,La,Nd,Th)PO4], as a source of light REEs, and/or xenotime (YPO4), as a potential source of Y and heavy REEs. The light minerals (gangue) in heavy minerals sands are dominated by quartz sand, clay minerals, and silt-size quartz and iron-oxide minerals. Feldspars are typically minor or absent constituents. Carbonate minerals are rare.

Mineralogical characteristics in beach placer deposits vary from region to region depending on the host rocks, their provenance, ambient climate, mechanism of transport, and the hydraulic conditions during the depositional stage (Borreswara Rao, 1957; Force, 1976, 1991). The roles of aeolian and marine processes along with the local hydrodynamic conditions and coastal geomorphology have a dominant role in the distribution of the placer minerals, as demonstrated along coastal Orissa, India (Komar and Wang, 1984).

Fig. 10.

Chondrite-normalized plot showing the REE distribution in selected monazites separated from heavy mineral sands deposits from a few continents. Chondrite-normalized europium values that lie below the trend of the other REEs are typical of monazite, but are not universal, as displayed by the monazite sample from a heavy mineral sand deposit in Taiwan. Data from Mukherjee (2007). Chondrite REE concentrations from Boynton (1984).

Fig. 10.

Chondrite-normalized plot showing the REE distribution in selected monazites separated from heavy mineral sands deposits from a few continents. Chondrite-normalized europium values that lie below the trend of the other REEs are typical of monazite, but are not universal, as displayed by the monazite sample from a heavy mineral sand deposit in Taiwan. Data from Mukherjee (2007). Chondrite REE concentrations from Boynton (1984).

Fig. 11.

Discrimination diagram plot of eTh/eU vs. eTh/eK in bulk sand samples collected from the Gopalpur and Rushikulya beach placer deposits, Orissa, India. The vertical bars represent values of eTh/eU = 2 or 7. Diagram modified from Sulekha Rao et al. (2009).

Fig. 11.

Discrimination diagram plot of eTh/eU vs. eTh/eK in bulk sand samples collected from the Gopalpur and Rushikulya beach placer deposits, Orissa, India. The vertical bars represent values of eTh/eU = 2 or 7. Diagram modified from Sulekha Rao et al. (2009).

Geochemistry

Trace elements associated with heavy mineral placers primarily include Ti, Hf, the REEs (such as La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) and Y, Th, and U. These elements have been used from the analyses of stream sediments to evaluate the presence of heavy mineral sands on a regional scale (e.g., Grosz, 1993). These pathfinder (exploration) elements reflect the composition of the potentially economic heavy minerals of this deposit type, including ilmenite (FeTiO3), rutile (TiO2), zircon ((Zr,Hf,U)SiO4), monazite ((La,Ce,Th,U)PO4), and xenotime (YPO4). Monazite is preferentially enriched in the light REEs relative to the heavy REEs (Fig. 10).

Variation in chemistry at a deposit scale most likely indicates the variations in heavy mineral content rather than geochemical gradients due to hypogene, hydrothermal, or supergene processes. Hydrothermal alteration and other forms of geochemical diffusion that are typical of most ore deposits are not associated with heavy mineral sands.

The thorium to uranium ratio is useful in the recognition of “geochemical facies” (Macfarlane et al., 1990) and a possible indicator of oxidizing and reducing conditions (Adams and Weaver, 1958; Anjos et al, 2006). Average equivalent Th/ equivalent U (eTh/eU) ratios for Gopalpur and Rushikulya beach samples, India (Figs. 6, 7), are observed to be in the range of 22 to 49 (Fig. 11). Both sets of beach samples lie in heavy mineral and clay mineral fields, indicating a generally higher presence of thorium in Gopalpur and higher potassium in Rushikulya. This could be attributed to adsorption and the chemical composition in this region (Doveton and Presnky, 1992). The detailed mechanism has been discussed by Sulekha Rao et al. (2009).

Higher concentrations of radioactive elements (Th, U) and REEs (La, Ce and Nd) have been observed in the monazite sands of Chhatrapur, India (Mohanty et al., 2003a). The chondrite-normalized REE distribution pattern of the monazite grains indicated uniformly enriched light REEs, which has been attributed to the preferential incorporation of lighter lanthanides formed during partial melting. The majority of the beach samples studied fall in both heavy minerals and clay mineral fields (Fig. 11). However, samples of beach sands from Gopalpur fall primarily in the heavy minerals field while Rushikulya beach samples plot mainly in the clay minerals field, indicating that both Th and K are associated with clay minerals due to adsorption and chemical composition (Doveton and Presnsky, 1992).

Most of the earlier studies on monazite REE chemistry are either related to igneous or metamorphic rocks, with few studies reported on placers. Geochemical studies of the REE chemistry in placers are important because sustained mining of placer deposits depletes their reserves. An important additional aspect is to utilize better techniques for enhanced recovery of the REEs from beach washings.

Typically, monazite extracted from beach placers is preferentially enriched in the light REEs. Dawood and El-Naby (2007) reported light REE enrichment from Sinai beach, Egypt. This monazite is sourced primarily by pegmatites and granites. The chondrite-normalized REE pattern from zircons (Fig. 12) of the Kanayakumari beach areas, located on the southernmost tip of India, exhibits light REE enrichment compared to heavy REE as well as Ce and Eu anomalies (Angusamy et al., 2004); these monazites are thought to be sourced by charnockites. Chhatrapur monazite placers in Orissa, on the east coast of India (Fig. 6), also show similar trends of light REE enrichment in zircons (Fig. 13) relative to heavy REEs as well as an Eu anomaly (Mohanty et al., 2003b). Chondrite-normalized REE fractionation patterns for the lunar and terrestrial monazite indicate that the light REEs (ie., La to Sm) are highly enriched relative to heavy REEs (i.e., Gd to Lu; Lovering et al., 1974).

Fig. 12.

Chondrite-normalized pattern of REEs in zircons from Kanyakumari beach placers, showing Ce and Eu anomalies (Angusamy et al., 2004).

Fig. 12.

Chondrite-normalized pattern of REEs in zircons from Kanyakumari beach placers, showing Ce and Eu anomalies (Angusamy et al., 2004).

Genesis of Heavy Mineral Placers

Whether the ultimate deposition of the heavy mineral-rich sediments occurs in an alluvial or coastal setting, the processes that form these deposits begin inland. High-grade metamorphic rocks (of amphibolite facies and higher) and a variety of plutonic igneous rocks are the principal sources of heavy minerals, including monazite. These bedrocks weather and erode, contributing detritus composed of sand, silt, clay, and heavy minerals to fluvial systems. Streams and rivers carry the detritus to the coast, where they are deposited in a variety of coastal environments, including deltas, the beach face (foreshore), nearshore, barrier islands, dunes, or tidal lagoons, as well as the channels and floodplains of streams and rivers in the coastal plain. The sediments are worked by the actions of waves, tides, longshore currents, and wind, which are effective mechanisms for sorting the mineral grains based on differences in their size and density. The finest-grained, most dense heavy minerals are the most effectively sorted. The result is that heavy minerals accumulate together, forming laminated or lens-shaped packages of sediments several meters and as much as tens of meters thick that are rich in heavy minerals. Generally, economic deposits of heavy mineral sands contain at least 1% total heavy mineral content. Most economic deposits of coastal heavy mineral sands (coastal placers) are Paleogene, Neogene, and Quaternary deposits, as well as some modern coastal deposits.

Fig. 13.

Chondrite-normalized pattern of the light REEs in zircons from Chhatrapur beach, India, showing LREE enrichment and Eu anomaly (after Mohanty et al., 2003a).

Fig. 13.

Chondrite-normalized pattern of the light REEs in zircons from Chhatrapur beach, India, showing LREE enrichment and Eu anomaly (after Mohanty et al., 2003a).

Factors influencing the formation of placer deposits

Climate: Climate influences the weathering processes, and ultimately decomposes the rock matrix and liberates the minerals. Tropical to subtropical climates promote chemical weathering, which has given rise to a decomposed stage of crystalline rocks called laterites. This could be considered as the preconcentration process of the placer minerals. Most of the rich, modern placer deposits of the world are in tropical regions.

Drainage pattern: Fluvial processes act as a conductor of sediment transport from the source rock to the zone of concentration. The erosive power of rivers is strong, releasing heavy minerals from the parent rock and transporting them downstream. For example, in the Kerala State of southwestern India, west-flowing rivers with steep gradients were the major agent of erosion and transportation of sediments to the Arabian Sea. Coastal processes: Beach deposits result from the interplay of coastal hydrodynamics of rivers, waves, and currents. The direction and strength of the coastal currents along with the geomorphology of the coast, sometimes influenced by localized faulting, determine the location of the deposit. Strong, sustained wave action moves sand from offshore to the shore. Waves sort out the heavy minerals based on their size and specific gravity, respectively. Studies suggest that mineral sorting occurs mainly on the upper part of the high-tide swash (wave) zone. Finegrained sands and heavy minerals on the foreshore (beach face) can be remobilized by winds, forming heavy mineral-rich sand dunes behind the beach. Sea-level changes are a function of climatic changes, such as ice ages. Rises in regional sea level (transgression) and fall of sea level (regression) strongly influence the deposition and preservation of heavy mineral sands, both along the strandline and inland fluvial deposits. Major episodes of heavy mineral sands accumulation have been linked to seaward progradation of the shore during regression events as well as prolonged transgressive events.

Exploration Considerations

Beach placer deposits—also referred to as “heavy mineral sands”—are well known from different parts of the world (Mero, 1965). Discoveries of beach placer deposits occurred along the Brazilian coast (Da Silva, 1979), China (Highley et al., 1988), Egypt, France, Bangladesh, and Iran (UNSCEAR, 1993). The beach placer deposits have primarily been investigated for their economic resources of heavy minerals, in particular ilmenite, rutile, zircon, sillimanite and garnet, apart from monazite and zircon and their actinide and rareearth elements. Two basic criteria provide the foundation for locating significant deposits of heavy mineral sands (placers) in coastal environments: (1) identify bedrock terranes that contain abundant high-grade metamorphic rocks or igneous rocks; and (2) identify ancient or modern coastal plains sourced by streams and rivers that drain these terranes.

For several decades, the mineable (economic) deposits of heavy mineral sands are those formed during the Paleogene, Neogene, or Quaternary. Heavy mineral deposits of Cretaceous age or older are likely to be hosted by lithified, wellcemented sandstones. Thus, restricting the assessment areas to unconsolidated Paleogene, Neogene, and Quaternary sediments deposited in coastal environments is a first-level exploration and assessment guideline.

Detailed geologic mapping that divides sedimentary units by time period (such as epoch) can benefit the search for deposits. For example, during the Pliocene many economic deposits of heavy mineral sands formed along the cratonic margins of widely separated continents. Also, within a single coastal basin, time-equivalent sedimentary units can indicate the extent of ancient strandlines, and thus the possible locations of related deposits.

Grosz (1993) described the application of stream sediments to locate deposits of heavy mineral sands in the mid-Atlantic coastal plain of the United States. His study analyzed concentrations of Ti, Hf, the REEs, Th, and U in stream sediments. These pathfinder (exploration) elements were selected to detect the presence of the heavy minerals typical of this deposit type, including ilmenite (FeTiO3), rutile (TiO2), zircon ((Zr,Hf,U)SiO4), monazite ((Ce,La,Y,Th,U)PO4), and xenotime (YPO4). Grosz (1993) concluded that geochemical data may be used to locate deposits of heavy minerals, especially by indicating areas in the mid-Atlantic region of the eastern United States that merit more detailed sampling and analyses.

Monazite-Bearing Beach Placer Deposits and Natural Radioactivity

Radiometric methods of geophysical exploration are useful in discovering and delineating deposits of heavy mineral-rich beach placers (heavy mineral sands). Several minerals in these deposits can produce a radiometric anomaly, in particular monazite, due to its thorium content (Force et al., 1982; Grosz et al., 1989, 1992; Grosz and Schruben, 1994). Zircon grains may also generate thorium and uranium anomalies. Potassium-bearing minerals, such as K-feldspar and micas, can also contribute to total count surveys, appearing as K highs in the gamma spectra.

A factor that is equally important is the potential radiation dose to humans and others from some high-grade placers, specifically, the exposure to natural radioactivity caused by the radioactive minerals in these deposits, principally monazite and zircon. The Erasama and Chhtarapur placer districts in the Orissa State along the east coast of India (Figs. 57) have been shown to be “high background radiation areas,” primarily due to the presence of thorium and uranium (Mohanty et al., 2004; Sengupta et al., 2005). Similarly, in Brazil the Guarapari coastline of Espírito Santo is a popular tourist destination known for its white sand beaches, but this shoreline is also known for its very high level of background radioactivity due to abundant detrital monazite.

The Significance of Monazite Placers

Monazite hosted by placer deposits offers several advantages. First, it has a two-fold value as an ore mineral—it contains several rare earth elements as well as thorium. Second, grains of monazite in placer deposits are mingled with other minerals of industrial value, such as ilmenite, rutile, zircon, garnet, sillimanite, and other heavy minerals; thus, monazite is recovered as a low-cost coproduct. Third, monazite is resistant to mechanical and chemical degradation and is typically the heaviest (highest density) mineral in the sand-silt deposit; these qualities make monazite relatively easy to mechanically separate and recover from heavy mineral sands.

Thorium has wide applications apart from its potential use as source of nuclear energy (International Atomic Energy Agency, 2005; Hongjie, 2012), such as its use in glasses of high refractive indices and as a source of neutrons. The major applications of thorium presently are in refractory usage, aerospace alloys, ceramics, and lighting. Thorium’s host minerals—monazite, thorite, thorianite, bedafite and zircon—are normally associated with other minerals that have a better control on the ore grade rather than thorium itself (Dill, 2010).

Because of the effect of the natural radiation environment and its enhancement due to the presence of monazite and the zircon in these placers, there is dire need to quantify the radiation background and its possible effects on the population. These studies are more so because quite a large number of beach placer areas, such as Gopalpur and other adjacent beaches, are also famous beach resorts of the southern part of coastal Orissa (east coast of India). Recently, these beach areas have become important centers of tourism with a large influx of people throughout the year (Mohanty et al., 2003a).

China, Japan, and the United States constitute about 90% of global product manufacturing that involves the REEs. The product distribution differences among the countries are substantial. Automobile catalytic converters accounted for 32% of rare earth use in the United States in 2007; the second biggest use was in metallurgical additives and alloys (around 21%). Japan used 28 and 27% of total rare earths in permanent magnets and polishing powders, and 15% in automobile catalytic converters. China has experienced the most dramatic changes in recent REE use. China has traditionally employed rare earths in applications such as metallurgical additives and alloys, petroleum refining, and glass and ceramics, but new applications in China have grown significantly since 2002. The end-use history demonstrates the dramatic increase in these new applications, which are primarily permanent magnets, polishing powders, nickel hydride batteries, phosphors, and automobile catalytic converters.

PIXE and EDXRF analyses on monazite sands from Chhatrapur and Erasama (Figs. 57) indicate the higher abundance of the oxides of cerium followed by lanthanum and neodymium. Cerium has wide applications, mainly in the fields of specialty glasses and ceramics. In addition, cerium lasers are used to locate atmospheric pollutants such as ozone and sulfur dioxide. Cerium compounds are also used to make phosphors. The primary uses of lanthanum are in hybrid car batteries, hydrogen sponge alloys, “mischmetal” (an alloy with approximate composition of 50% Ce, 25% La, and the remainder mostly Nd and Pr), and in cerium-doped lanthanum-based scintillators. Lanthanum is also used to enhance the alkali resistance of glasses, such as infrared absorbing glasses. Neodymium is useful in crycoolers and frequently used in countries such as China as a fertilizer. In addition, neodymium compounds are used in manufacturing neodymium magnets, which are the strongest permanent magnets at this time.

The sector with the largest consumption use of REEs is metallurgical applications—mainly in the form of mischmetal.

With the growing demand for Nd and Pr in magnets, current processing methods sometimes recover those elements individually, leaving a mischmetal composition consisting almost entirely of Ce and La. The sector with the next highest use of REEs is computer components, which contain Nd, Pr, Dy, Gd, and Tb. Automobile catalytic converters rank third among rare earth consumption, mostly using Ce. Six other product sectors are also significant users of REEs: audio systems (mostly Ce), glass additives (Ce and La), nickel metal hydride batteries for computers (Nd, Pr, Dy, and Tb), catalysts (predominantly La), automobiles (Nd and Pr), and wind turbines (Nd and Pr). Together, the consumption of REEs in these nine product sectors constitutes nearly 88% of the total REE use (Du and Graedel, 2011).

Heavy mineral placers offer several advantages as sources of mineral feedstock:

  1. The deposits are usually unconsolidated or weakly consolidated sediments, and thus relatively easy to excavate;

  2. These deposits are sizeable, with orebodies of at least 10 Mt;

  3. Well-established techniques are used to separate the heavy minerals from the ore body (mixture of sand-silt-clay);

  4. A single deposit and operation can produce multiple salable products, such a Ti oxide minerals (ilmenite, rutile), zircons, garnet, staurolite, tourmaline, kyanite, and/or sillimanite, as well as monazite, a potential source of the light REEs and thorium.

An aspect of utmost significance is the depletion of heavy mineral content and the associated rare earth minerals due to continuous mining of the beach placers. Thus, additional deposits of heavy minerals (including inland paleodeposits) will be needed to fill increasing world demand for many industrial minerals, REEs, and perhaps thorium.

Disclaimer

Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

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Figures & Tables

Fig. 1.

Global map showing significant placer districts (red squares) that produced monazite and/or xenotime in the past or presently; these minerals were recovered as by- or coproduct commodities with other economic heavy minerals. Current monazite production occurs at modern beach placers in India and coastal placers at the Buena district, Brazil.

Fig. 1.

Global map showing significant placer districts (red squares) that produced monazite and/or xenotime in the past or presently; these minerals were recovered as by- or coproduct commodities with other economic heavy minerals. Current monazite production occurs at modern beach placers in India and coastal placers at the Buena district, Brazil.

Fig. 2.

Index map of southern India and northern Sri Lanka, showing locations of (1) historic and active heavy mineral sands operations discussed in this report, and (2) areas of Quaternary and Neogene sediments.

Fig. 2.

Index map of southern India and northern Sri Lanka, showing locations of (1) historic and active heavy mineral sands operations discussed in this report, and (2) areas of Quaternary and Neogene sediments.

Fig. 3.

Index map of Australia showing the Cenozoic sedimentary basins and other districts (red dots; Tiwi Islands, Cape York, North Stradbroke Island) that host deposits of heavy mineral sands that are currently being mined.

Fig. 3.

Index map of Australia showing the Cenozoic sedimentary basins and other districts (red dots; Tiwi Islands, Cape York, North Stradbroke Island) that host deposits of heavy mineral sands that are currently being mined.

Fig. 4.

Index map showing monazite-producing placer deposits (red squares) along the central coastline of Brazil. The active monazite producer is the Buena district (Industrias Nucleares do Brasil SA (INB), 2013), the southernmost placer district shown in the map.

Fig. 4.

Index map showing monazite-producing placer deposits (red squares) along the central coastline of Brazil. The active monazite producer is the Buena district (Industrias Nucleares do Brasil SA (INB), 2013), the southernmost placer district shown in the map.

Fig. 5.

Map showing the sample locations in the Erasama beach placer deposit, Orissa, India (after Mohanty et al., 2004).

Fig. 5.

Map showing the sample locations in the Erasama beach placer deposit, Orissa, India (after Mohanty et al., 2004).

Fig. 6.

Map showing sample locations in the Chhatrapur beach placer deposit, Orissa, India (after Mohanty et al., 2004).

Fig. 6.

Map showing sample locations in the Chhatrapur beach placer deposit, Orissa, India (after Mohanty et al., 2004).

Fig. 7.

Index map of the Rushikulya beach placer deposit along the Orissa coast, southeast India, showing sample locations (after Sulekha Roa et al., 2009).

Fig. 7.

Index map of the Rushikulya beach placer deposit along the Orissa coast, southeast India, showing sample locations (after Sulekha Roa et al., 2009).

Fig. 8.

Map of monazite-bearing alluvial placers in North and South Carolina, United States. Modified from Staatz et al. (1979).

Fig. 8.

Map of monazite-bearing alluvial placers in North and South Carolina, United States. Modified from Staatz et al. (1979).

Fig. 9.

Generalized map of known monazite-bearing alluvial placer districts in Idaho. Modified from Staatz et al. (1980).

Fig. 9.

Generalized map of known monazite-bearing alluvial placer districts in Idaho. Modified from Staatz et al. (1980).

Fig. 10.

Chondrite-normalized plot showing the REE distribution in selected monazites separated from heavy mineral sands deposits from a few continents. Chondrite-normalized europium values that lie below the trend of the other REEs are typical of monazite, but are not universal, as displayed by the monazite sample from a heavy mineral sand deposit in Taiwan. Data from Mukherjee (2007). Chondrite REE concentrations from Boynton (1984).

Fig. 10.

Chondrite-normalized plot showing the REE distribution in selected monazites separated from heavy mineral sands deposits from a few continents. Chondrite-normalized europium values that lie below the trend of the other REEs are typical of monazite, but are not universal, as displayed by the monazite sample from a heavy mineral sand deposit in Taiwan. Data from Mukherjee (2007). Chondrite REE concentrations from Boynton (1984).

Fig. 11.

Discrimination diagram plot of eTh/eU vs. eTh/eK in bulk sand samples collected from the Gopalpur and Rushikulya beach placer deposits, Orissa, India. The vertical bars represent values of eTh/eU = 2 or 7. Diagram modified from Sulekha Rao et al. (2009).

Fig. 11.

Discrimination diagram plot of eTh/eU vs. eTh/eK in bulk sand samples collected from the Gopalpur and Rushikulya beach placer deposits, Orissa, India. The vertical bars represent values of eTh/eU = 2 or 7. Diagram modified from Sulekha Rao et al. (2009).

Fig. 12.

Chondrite-normalized pattern of REEs in zircons from Kanyakumari beach placers, showing Ce and Eu anomalies (Angusamy et al., 2004).

Fig. 12.

Chondrite-normalized pattern of REEs in zircons from Kanyakumari beach placers, showing Ce and Eu anomalies (Angusamy et al., 2004).

Fig. 13.

Chondrite-normalized pattern of the light REEs in zircons from Chhatrapur beach, India, showing LREE enrichment and Eu anomaly (after Mohanty et al., 2003a).

Fig. 13.

Chondrite-normalized pattern of the light REEs in zircons from Chhatrapur beach, India, showing LREE enrichment and Eu anomaly (after Mohanty et al., 2003a).

Major Coastal and Fluvial Thorium (Monazite) Placer Deposits

Table 1.
Major Coastal and Fluvial Thorium (Monazite) Placer Deposits
Country State Placer district Latitude Longitude Comments References
Australia Western Australia Eneabba, Perth basin -29.79 115.30 About 2,5001 of monazite produced annually as a coproduct prior to 1995 Sheppard (1990);
Castor and Hedrick (2006)
Brazil Bahia Alcobaga -17.26 -39.22 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Espírito Santo Anchieta (Parati, Imbiri,Pipa de Viho, Maeba) -20.77 -40.57 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Espírito Santo Aracruz -19.95 -40.15 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Sergipe Brejo Grande - Pacatuba -10.43 -36.47 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Rio de Janeiro Buena (Buena Norte, Buena Sol) -21.52 -41.07 Active producer of monazite from beach placers Industrias Nucleares do Brasil SA (2013)
Brazil Rio Grande do Norte Camaratuba -6.89 -34.89 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Bahia Cumuruxatiba (Curumuxatiba, Comoxatiba) -18.31 -39.66 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Espírito Santo Guarapari (Praia do Vaz, Vila Velha, Rastinga, Canto do Riacho, Praia de Diogo) -20.70 -40.51 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Espírito Santo Itapemirim (Boa Vista, Siri) -21.17 -40.91 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Paraiba Mataraca -6.48 -34.97 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Bahia Porto Seguro district -16.43 -39.08 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Bahia Prado area -17.39 -39.21 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Rio de Janeiro Sao Joao de Barra (Barra Sao Joao) -21.40 -41.00 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Espírito Santo Serra (Jacareipe) -20.17 -40.19 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Bahia, Espirito Santo Vitoria -18.33 -39.66 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
China Guangxi Beihei 21.48 109.10 River and coastal placers; byproduct monazite Jackson and Christiansen (1993); Orris and Grauch (2002)
China Guangdong Dianbai 21.50 111.02 Coastal placers; by-product monazite Jackson and Christiansen (1993); Orris and Grauch (2002)
China Guangdong Haikang 20.98 110.07 River and coastal placers; by-product monazite Jackson and Christiansen (1993); Orris and Grauch (2002)
China Guangdong Nanshanhai 21.55 111.67 Coastal placers; by-product monazite Jackson and Christiansen (1993); Orris and Grauch (2002)
China Hainan Island Sai-Lao, Wuzhaung, and Xinglong districts 18.68 110.38 Coastal placers; by-product monazite Jackson and Christiansen (1993); Orris and Grauch (2002)
China Guangxi Xun Jiang 23.50 110.83 River placers; by-product monazite Jackson and Christiansen (1993); Orris and Grauch (2002)
India Orissa Erasama 20.15 86.51 Coastal placers containing monazite Mohanty et al. (2003a, b, 2004)
India Orissa Chhatrapur 19.34 85.01 Coastal placers containing monazite Mohanty et al. (2003a, b, 2004)
India Andhra Pradesh Visakhapatnam 17.66 83.27 Coastal placers containing monazite Raju et al. (2001)
India Kerala Manavalakurichi 8.14 77.30 Coastal placers containing monazite Tipper (1914); Raju et al. (2001)
India Kerala Chavara 8.99 76.52 Coastal placers containing monazite Prakash et al. (1991)
India Maharashtra Ratnagiri 17.02 73.28 Coastal placers containing monazite Raju et al. (2001)
Malaysia Selangor Batang Berjuntai 3.39 101.42 Fluvial tin placers; by-product monazite and xenotime Orris and Grauch (2002)
Sri Lanka Eastern Province Pulmoddai 8.95 80.99 Coastal placers containing monazite Lanka Mineral Sands Limited (2013)
Thailand Phang-nga Takua-Pa 8.87 98.35 Fluvial tin placers; by-product monazite and xenotime Economic and Social Commission for Asia and the Pacific (2001)
United States Idaho Central Idaho fluvial placers 44.42 -116.02 Fluvial placers; by-product monazite Staatz et al. (1980)
United States North Carolina and South Carolina Piedmont region fluvial placers 35.31 -81.54 5,0001 of monazite produced from 1887 to 1917 Overstreet et. al. (1968); Staatz et al. (1979)
United States Florida Mineral City 30.24 -81.39 About 11 of monazite produced in 1925 Staatz et al. (1980)
United States Florida Rutile Mining Co. mine 30.34 -81.60 Small amounts of monazite recovered from beach sands Staatz et al. (1980)
United States Florida Riz Mining Co. mine 27.64 -80.35 Dune sands; monazite as by-product from 1940s to 1955 Staatz et al. (1980)
United States Florida Green Cove Springs 29.87 -81.71 Beach deposits; monazite recovered as coproduct Staatz et al. (1980); Castor and Hedrick (2006)
United States Florida Boulogne 30.77 -81.98 Beach deposits; monazite recovered as coproduct Staatz et al. (1980)
Country State Placer district Latitude Longitude Comments References
Australia Western Australia Eneabba, Perth basin -29.79 115.30 About 2,5001 of monazite produced annually as a coproduct prior to 1995 Sheppard (1990);
Castor and Hedrick (2006)
Brazil Bahia Alcobaga -17.26 -39.22 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Espírito Santo Anchieta (Parati, Imbiri,Pipa de Viho, Maeba) -20.77 -40.57 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Espírito Santo Aracruz -19.95 -40.15 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Sergipe Brejo Grande - Pacatuba -10.43 -36.47 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Rio de Janeiro Buena (Buena Norte, Buena Sol) -21.52 -41.07 Active producer of monazite from beach placers Industrias Nucleares do Brasil SA (2013)
Brazil Rio Grande do Norte Camaratuba -6.89 -34.89 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Bahia Cumuruxatiba (Curumuxatiba, Comoxatiba) -18.31 -39.66 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Espírito Santo Guarapari (Praia do Vaz, Vila Velha, Rastinga, Canto do Riacho, Praia de Diogo) -20.70 -40.51 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Espírito Santo Itapemirim (Boa Vista, Siri) -21.17 -40.91 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Paraiba Mataraca -6.48 -34.97 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Bahia Porto Seguro district -16.43 -39.08 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Bahia Prado area -17.39 -39.21 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Rio de Janeiro Sao Joao de Barra (Barra Sao Joao) -21.40 -41.00 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Espírito Santo Serra (Jacareipe) -20.17 -40.19 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
Brazil Bahia, Espirito Santo Vitoria -18.33 -39.66 Coastal placer; past producer of monazite Overstreet (1967); Orris and Grauch (2002)
China Guangxi Beihei 21.48 109.10 River and coastal placers; byproduct monazite Jackson and Christiansen (1993); Orris and Grauch (2002)
China Guangdong Dianbai 21.50 111.02 Coastal placers; by-product monazite Jackson and Christiansen (1993); Orris and Grauch (2002)
China Guangdong Haikang 20.98 110.07 River and coastal placers; by-product monazite Jackson and Christiansen (1993); Orris and Grauch (2002)
China Guangdong Nanshanhai 21.55 111.67 Coastal placers; by-product monazite Jackson and Christiansen (1993); Orris and Grauch (2002)
China Hainan Island Sai-Lao, Wuzhaung, and Xinglong districts 18.68 110.38 Coastal placers; by-product monazite Jackson and Christiansen (1993); Orris and Grauch (2002)
China Guangxi Xun Jiang 23.50 110.83 River placers; by-product monazite Jackson and Christiansen (1993); Orris and Grauch (2002)
India Orissa Erasama 20.15 86.51 Coastal placers containing monazite Mohanty et al. (2003a, b, 2004)
India Orissa Chhatrapur 19.34 85.01 Coastal placers containing monazite Mohanty et al. (2003a, b, 2004)
India Andhra Pradesh Visakhapatnam 17.66 83.27 Coastal placers containing monazite Raju et al. (2001)
India Kerala Manavalakurichi 8.14 77.30 Coastal placers containing monazite Tipper (1914); Raju et al. (2001)
India Kerala Chavara 8.99 76.52 Coastal placers containing monazite Prakash et al. (1991)
India Maharashtra Ratnagiri 17.02 73.28 Coastal placers containing monazite Raju et al. (2001)
Malaysia Selangor Batang Berjuntai 3.39 101.42 Fluvial tin placers; by-product monazite and xenotime Orris and Grauch (2002)
Sri Lanka Eastern Province Pulmoddai 8.95 80.99 Coastal placers containing monazite Lanka Mineral Sands Limited (2013)
Thailand Phang-nga Takua-Pa 8.87 98.35 Fluvial tin placers; by-product monazite and xenotime Economic and Social Commission for Asia and the Pacific (2001)
United States Idaho Central Idaho fluvial placers 44.42 -116.02 Fluvial placers; by-product monazite Staatz et al. (1980)
United States North Carolina and South Carolina Piedmont region fluvial placers 35.31 -81.54 5,0001 of monazite produced from 1887 to 1917 Overstreet et. al. (1968); Staatz et al. (1979)
United States Florida Mineral City 30.24 -81.39 About 11 of monazite produced in 1925 Staatz et al. (1980)
United States Florida Rutile Mining Co. mine 30.34 -81.60 Small amounts of monazite recovered from beach sands Staatz et al. (1980)
United States Florida Riz Mining Co. mine 27.64 -80.35 Dune sands; monazite as by-product from 1940s to 1955 Staatz et al. (1980)
United States Florida Green Cove Springs 29.87 -81.71 Beach deposits; monazite recovered as coproduct Staatz et al. (1980); Castor and Hedrick (2006)
United States Florida Boulogne 30.77 -81.98 Beach deposits; monazite recovered as coproduct Staatz et al. (1980)

Contents

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