Rare Earth Elements: A Review of Production, Processing ...

Rare Earth Elements Review Section 3 – Life-Cycle Stages of Rare Earth Elements Mines
3.3.2.1 Exploration
Mineral exploration includes any activity performed to discover a potential ore reserve and determine the
location, size, shape, position, and current economic value of the deposit. Prospecting, staking, sampling,
assessment of mineral potential and economic feasibility, development plan, and permitting are all steps
and activities that can be considered as part of the exploration stage. Prospecting employs non-invasive
methods to evaluate the presence and characteristics of a potential deposit. Staking establishes mineral
rights to develop the mine. An exploration step, using more sophisticated methods to delineate the deposit
(e.g., geophysics), is followed by an intermediate stage of exploration that uses invasive methods (e.g.,
trenching, core or rotary drilling, bulk sampling) to sample the deposit. Samples are analyzed for metal
content, and the data collected from the previous steps are used to create mineral potential maps showing
the geologic favorability of the deposit; definition drilling is generally performed during this advanced
stage of exploration. If the deposit is proven economically viable, then a mining development plan is
drafted and applicable permits are obtained. These steps can also be considered as independent stages
with exploration (i.e., use of invasive assessment methods) as one of these steps. As previously
mentioned, the resource evaluation and scoping of the deposit can also be performed during the mine
design stage. Baseline environmental studies may be conducted, if required, prior to exploration to
determine the presence of sensitive species and habitat that might be impacted during these activities.
Exploration Methods
The approach and methodology used for exploration depend upon various factors, such as terrain, nature,
and size of the target, and expected depth of the ore body; regulatory and permitting requirements and
restrictions; available information and technology; and available capital resources. The intent of the
exploration company (e.g., prove the deposit for sale, develop the mine) will also influence the scope of
the initial exploration project and the approach and methods used to prove the deposit. The methods used
may be very simple and low cost, or technically sophisticated.
The location of a proposed mine will also influence the extent and type of exploration activities that can
occur. If the deposit is located in an existing mining district and/or on privately owned lands, then drilling
permits may be more easily obtained by the exploration or mining company, and more aggressive
exploration (e.g., exploratory drilling) may occur. If the site of the deposit is located near, for example,
national forest lands, then exploration activities requiring land disturbance may not be allowed until a
preliminary environmental information document (EID) is completed and undergoes EPA/NEPA review.
Upon approval by the EPA or state agencies, drilling data can be collected and analyzed. The exploration
data would then be used to inform additional environmental assessment that may be needed in the mine
development-construction stage. The environmental impacts of exploration activities are sometimes
overlooked; however, in many states, permits are required. An example (U.S. EPA, 2011b) is in the state
of Alaska, where permits required for exploration activities include a Clean Water Act 404 permit for
wetlands disturbance; camp permits; a temporary water use permit; an overland travel permit; land-use
permits for off-claim camps or staging areas; bonds for staging fuel; hardrock exploration land-use
permit; and a state bond pool requirement for reclamation. Drilling and trenching can be extensive, longterm
operations using multiple types of heavy equipment with associated waste (e.g., used vehicle fluids,
lubricants and greases, solvents, other traditional industrial materials). Additionally, mining-type wastes
(e.g., waste rock) can be produced during exploration activities and will need to be managed.
Passive Mine Exploration Methods
Examples of passive exploration methods applicable to rare earth deposits include common prospecting
approaches (e.g., water, rock, soil, and sediment sampling; shallow pits) and geologic mapping and
general field investigations. More sophisticated techniques employ geophysics, aerial and satellite remote
sensing, mineral deposit models, and potentially other geochemical testing methods. The exploration team
will generally attempt to identify geochemical and geophysical signatures that suggest the presence of the
3-6