Geobotanical prospecting isprospecting based on the composition and health of surroundingbotanical life to identify potential resource deposits.[1] Using a variety of techniques, includingindicator plant identification,[2]remote sensing[3] and determining the physical and chemical condition of the botanical life in the area,[4][5] geobotanical prospecting can be used to discover different minerals. This process has clear advantages and benefits, such as being relatively non-invasive and cost efficient.[2][3] However, the efficacy of this method is not without question. There is evidence that this form ofprospecting is a valid scientific method, especially when used in conjunction with otherprospecting methods.[6][2] But as identification of commercial mines are invariably guided bygeological principles and confirmed bychemical assays, it is unclear as to whether this prospecting method is a valid standalone scientific method or an outdated method of the past.[7]
There is a complex interaction between soil and plants.[8] Thenutrient andmineral composition of the soil heavily influences both the type and physical condition ofbotanical life it can support.[8][9] Using this principle, in certain cases, it is theoretically possible to determine the mineral content of the underlying soils and rocks (i.e., mineral deposits) using the overlying botanical life.[10]
The technique has been used inChina since in the 5th century BC. People in the region noticed a connection between vegetation and the minerals located underground. There were particular plants that throve on and indicated areas rich in copper, nickel, zinc, and allegedly gold though the latter has not been confirmed. The connection arose out of an agricultural interest concerning soil compositions. While the process had been known to the Chinese region since antiquity, it was not written about and studied in the west until the 18th century in Italy.[11]
Geobotanical prospecting can be done through a variety of different methods. Any method that uses the overlying botanical life (in any way) as an indication of the underlying mineral composition can be considered geobotanical prospecting.[12] These methods can includeindicator plant identification,[2]remote sensing,[3] and determining the physical and chemical condition of the botanical life through laboratory techniques.[13][5]
Silene suecica. Indicator plant that was used by prospectors to discover ore deposits.
Indicator plant identification is determining the presence and distribution of certain indicator plants.[2] Certain plants prefer certain concentrations of minerals in the soil and would thus be more plentiful in areas with higher concentrations of their preferred mineral.[2][1] By mapping the distribution of indicator plants, it is possible to get an overview of the geology of the area.[2]
Aerial photography is simply taking photographs of the ground from ahigher elevation.[3] Using aerial photography it is possible to survey a large area of land relatively quickly at relatively low cost to get an overview of theplant diversity of an area.[3] This can lead to the mapping of underlying mineral deposits.[2][3]
For example, usingaerial photography, it is possible to determine the existence of prematureleaf senescence (premature aging of cells).[3] In some cases, this can lead to the detection of increased copper concentrations in the soil, leading to the discovery of copper deposits.[3]
Satellite imagery can be used to capture large amounts of data in a large area.[15] This data, when analyzed correctly, can be used to aid in the geobotanical prospecting process.[15][16] Satellite imagery can be used to determine concentrations of certain minerals and elements in certain plants.[17] For example, satellite imagery has been used to determinepotassium concentrations intea plants.[17] Satellite imagery has also been used to monitorinvasive plant movement.[18] Using satellite imagery, it is possible to get a detailed image of the overlying botanical life.[15][16] Using the overlying botanical life it is possible to get a overview of the underlying geological composition.[10][15]
As plants uptake minerals from their surrounding soils, the minerals get deposited into their tissues.[5] In alaboratory setting, plant tissues can be analyzed to determine the concentrations of these minerals.[19] Once the concentrations of these minerals are known, it is possible to determine the concentrations of minerals in these plants soils and thus the underlying geology of the area.[10] This method is particularly useful fornanoparticles i.e., particles that are too low in concentration to detect in soils but get fixed in plant tissue.[20] This is the case when prospecting for gold.[21]
Using thebotanical life in the area to determine the underlying geological composition has been used in a variety of ways and for a variety ofminerals.[1]
Copper (Cu) is an essentialmicronutrient that plants absorb from the soil.[22] Copper that is absorbed from the soil is used in various internal process such asphotosynthesis,plant respiration andenzyme function.[23] However, increased concentrations of copper can lead tocopper toxicity or copper mineralization in the plant, causing specific physiological responses.[24] This mineralization can then be detected through geobotanical surveys.[24]
Geobotanical prospecting for copper generally takes the form of identifyingindicator plants, i.e.,metallophyte species.[25]Metallophytes are plants that can tolerate high levels of heavy metals in the soils such as copper.[26] These metallophyte species can show symptoms ofcopper toxicity that can be detected through geobotanical methods likeremote sensing or field surveys.[3] These symptoms of copper toxicity can include altered photosynthesis cycles, stunted growth, discoloration and inhibition of root growth.[27][28]
Some popular examples of copper indicator plants include the Zambian copper flowerBecium centraliafricanum,[29]Haumaniastrum kutungense,[30][7] andOcimum centraliafricanum (syn.Becium homblei), a "most faithful" indicator plant, known as "copper plant" or "copper flower", found only on copper (and nickel) rich soils in central to southern Africa.[31][30] Lichens (Lecanora cascadensis) have also been used to determine copper mineralization.[32]
Geobotanical surveys for copper are most likely to consist of a variation of methods such asfield observations andremote sensing (aerial photography andsatellite imagery).[3][15] After potential copper rich areas are discovered through the methods such as those listed above, further exploration techniques can be used to confirm the presence ofmineral deposits.[3] These exploration techniques can include soil sampling andgeochemical analysis,[33][34]geophysical surveys anddrilling.[35][36] Geobotanical prospecting is a useful first step in the prospecting process for copper deposits, and its full potential can be reached when used in conjunction with other prospecting methods.[36][37]
Artemisia absinthium. A type of wormwood plant belonging to the genusArtemisia. The genus of plants most commonly used in geobotanical prospecting for gold.
Prospecting forgold using geobotanical methods usually involves determining the gold content that has been absorbed by botanical life.[21] However, because the gold content in soils and in the corresponding vegetation is usually very low (practically undetectable), direct measuring of gold is unlikely to be effective.[38][39] To overcome this obstacle, detecting a suitable pathfinder mineral is the method usually employed.[21] Pathfinder minerals (a mineral that almost always occurs in conjunction with another mineral) most commonly associated with gold isarsenic.[40] As for which plants are most likely to contain elevated levels of gold, shrubs from the genusArtemisia (sagebrush or wormwood) are recommended.[39]
Research has been ongoing for many years on the interaction between gold and vegetation.[10][41] These new methods could increase the accuracy of gold detection in vegetation.[41] However, presently because of the difficulties in identifying gold contained within vegetation, geobotanical prospecting for gold is most effective when combined with other prospecting methods likegeophysical surveys.[42][35]
Marchantia polymorpha. A species of bryophyte (liverwort). An example of the type of plant used for geobotanical prospecting of uranium.
Uranium is not an essential nutrient to plants, but if uranium is present in the surrounding soils the element will be taken up into the plant system.[8] Uranium is toxic to plants due to itsradioactive nature.[43] Plants that have accumulated a larger than normal amount of uranium, will show signs of uranium toxicity.[44] Uranium toxicity results in various physiological processes of the plants being hindered.[44][45] These hindered physiological processes includeseed germination andphotosynthesis.[citation needed] Because of these changes in physiology, uranium toxicity is relatively easy to detect in plants.[43]
Geobotanical prospecting for uranium deposits usually consists of rigorous systematic sampling of vegetation as well as laboratory analysis to determine uranium content.[46][47]
Geobotanical prospecting has also been used to discover a variety of other resources. One such resource isKimberlite pipes, an igneous rock feature that often containsdiamonds.[6] The indicator plant,Pandanus candelabrum, was found to be biochemically distinct when growing on kimberlite pipes when compared to samples growing oncountry rock.[48] This discovery makes it possible for future prospecting of kimberlite pipes and by association, diamonds, using geobotanical prospecting.[6][48]
In some cases direct detection of the mineral of interest is not possible, and detection of pathfinder minerals is required.[40] Such is the case witharsenic andgold,[40] and inscandium and ultramaficregolith's (rich incobalt andnickel).[49] In cases such as these, the mineral concentration in the local flora is especially useful.[49]
Pinus brutia. An indicator plant for iron and zinc.
There are many advantages and benefits associated with geobotanical prospecting, making it a valuable addition to modern andtraditional prospecting methods. It is a relatively cost effective method of prospecting when compared to traditional methods such asdrilling.[19] By taking advantage of the indications from local flora, it is possible to get an overview of the local geology.[52] This overview can be accomplished with a significantly lower investment in manpower and expensive equipment that is needed for more traditional prospecting methods such as drilling.[52][53] Geobotanical prospecting is a minimally invasive process, allowing for large scale initial prospecting with minimal environmental disruption.[3] Making it a relativelyenvironmentally sustainable prospecting method.[1]
Along with its minimally invasive nature, geobotanical prospecting allows for time efficient large-scale prospecting.[3] With continual advancements inremote sensing technologies such asaerial photography andsatellite imaging, it is possible to get a detailed map of an area's botany in a relatively short amount of time.[2] This large scale fast spatial coverage increases the likelihood of locating mineral deposits and resulting in successfulprospecting efforts.[52][15]
Another benefit of geobotanical prospecting is an educational one.[54] Mapping the vegetation of an area and determining its underlying geology, allows researchers to increase their understanding of the earthsgeochemical processes, i.e., the interaction betweenminerals and livingbotany.[52][54] By analyzing the distribution and concentration of various elements and minerals in botanical life, researcher's understanding of themineralization process will increase.[2] This rise in understanding will allow for a broader understanding of the interactions between inorganic substances, such as minerals, and organic life, such as plants.[54]
Geobotanical prospecting can be applied to many minerals, including copper and uranium.[24][46] This versatility is an advantage of geobotanical prospecting.[7]
Geobotanical prospecting is not without limitations. The success of geobotanical prospecting methods depends on many factors including, localplant species diversity,[2][1]soil composition[8] andclimate conditions.[3][55] All these factors can obscure key results or cause a misinterpretation of findings.
Plants have different appearance in different seasons. Any geobotanical prospecting methods relying on appearance will be season dependent.
One limitation is that this method relies on the presence of specific indicator plants, i.e., localplant species diversity.[1][7] The specific indicator plants needed to determine mineral deposits may not be established in every area where those mineral deposits are located.[55] These deposits would remain undetected if geobotanical prospecting was the only method of prospecting used.[7] Additionally, even if the indicator plants were present but the mineral deposit had not released enough minerals into the surrounding soils, thesoil composition of the area would not allow for indicator plants to intake sufficient concentrations of the desired minerals.[8] These deposits would remain undetected. Theremote sensing methods depend on climate conditions. Some indicator plants will not show all identifiable features in all seasons, i.e., some plants only bloom insummer andautumn.[55] If climate is not conducive to accurate results, mineral deposits may remain undetected.[3]
Pollutants will affect chemical composition of the soil. If the chemical composition is drastically affected, plant-soil interactions will change. This could cause changed in geobotanical prospecting methodology.
Asanthropogenic influences increase, vegetation-based indicators may be heavily influenced.[56] Asland use changes andpollution could alterplant-soil interactions and element uptake patterns, results from geobotanical prospecting ventures may be incorrectly interpreted.[8][56] The incorrect results could lead to misidentification of mineral deposits or missing mineral deposits altogether.[7]
Another limitation of geobotanical prospecting is that these methods requirespecialized expertise in bothgeology andbotany, two fields of expertise not commonly studied together.[5] In order to confirm results, samples need to be analyzed in laboratories which could require specialized equipment and expertise.[20]
Geobotanical prospecting will likely show the mostefficacy when integrated with other prospecting methods, such as geological andgeophysical data and surveys.[5][57][36]
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