Gold biogenesis - Oberto (2018)

AMI conference - Oberto Matteo - October 2018
1
Biogenic gold cycle - Potential in exploration and mining
1 cm
Australia (Ballarat)
279 oz (7,9 Kg)
Urali (Miass, Russia)
0,42 oz (11,98 g)
1 oz (ounce) = 28,35 g.
1 ozt (ounce troy) = 31,10 g.
@Bogni Giorgio, marzo 2018@L’OR Deluy N17
Biogenic gold cycle and mining exploration
Summary of the main issues related to the biogenic cycle of gold, genesis of biogenic nuggets,
mining exploration (geochemistry of heavy sediments, biogeochemistry, biosensing and bioleaching).
[1] [2]

2
Index:
- 1- Theoretical concepts: biogenic cycle of gold:
1 a- Introduction;
1 b- Potential of the biotic model: functioning of biofilms;
1 c- Biotic, abiotic model and comparison;
1 d- Influence of the biotic and abiotic model;
1 e- The role of vegetation associated with the biogenic cycle;
- 2- Potential in mining exploration:
2 a- Geochemistry of heavy sediments;
2 b- Geochemistry of soils and land adjacent to the DAP
(Auriferous Primary Deposit);
2 c- Biosensing and recognition of bacterial association;
- 3- Potential in mining :
3 a- Bioprocessing (Bioleaching);
- 4- Conclusions
- 5- Bibliography and sitography
@L’OR Deluy N17 [3]

3
- 1- Theoretical concepts: biogenic cycle of gold:
1 a- Introduction Bacteria are unicellular prokaryotic microorganisms[5], they possess some
characteristics:
Metabolic activities[5]
A certain number carries out pathogenic action, others participate in the
processes of enzymatic degradation of the remains of animals and plants
and the cycles of carbon, oxygen, hydrogen, nitrogen, sulfur, iron,
manganese, etc.
Morphology[5]
Bacteria show few basic forms[4]: spherical (cocchi), baston
(bacilli), curved (vibrions or spirilli). The smallest bacteria
observed to date (nanobacteria) have an average diameter of
200-500 nm.
[4]
Biogenic gold cycle - Potential in exploration and mining AMI conference - Oberto Matteo - October 2018

4
Reproduction and growth[5]
Bacteria reproduce by division of the mother cell into two daughter cells[6,7].
The dividing cell increases in volume, then begins to shrink at the median axis, until it separates
into two new identical identities[6]. These possibilities form characteristic groupings (chains,
tetrads, filaments, clusters, etc.).
The reproduction has an average duration of 20-30 minutes and depends on the bacterial
species examined[7].
[7][6]
6- detail of the moment in which the bacterium duplication takes place (lower portion of the image).
7-colony of bacteria that has taken root on a surface, called biofilm.

5
Bacterial communities[5]
The type of growth prevalent in natural environments is the sessile one. When nutrient intake is
limited, the bacteria tend to adhere to solid supports and remain stably attached to the solid-
liquid interface, where the nutrients are concentrated. Once established, the bacteria secrete
exopolysaccharide substances that surround them, guaranteeing their cohesion to the support
and to each other[5,8].
The whole process takes from a few days to a few weeks[5].
Genesis of biofilm
[8]
8- engraftment, expansion and reproduction of sessile bacteria through biofilms.
6. The cycle repeats
itself
4. Mature biofilm 5. Some cells break
away from the
biofilm to colonize
other surfaces
3. Bacterial
division, microbial
population growth
and
polysaccharide
matrix secretion
2. Bacterial cells
aggregate
1. Single bacterial
cells adhere to a
surface

6
Legend
9- SEM photographs (electronic scanning
microscope) of biofilm on the surface of
gold granules coming from:
A- Lively's find (Australia);
B- Corrego Born Sucesso (Brazil);
C- Australia (gold in nanophase);
D- Prophet Mine (Australia);
(Figure number 3 from Rea et alii., 2016)[9]

7
Theoretical concepts: biogenic cycle of gold
1b - Potential of the biotic model: functioning of biofilms
Legend
10- SEM photographs of biofilm on the surface of granules
Gold:
A, B - Growth and development of biofilm on gold granules
from «Black placer», Arizona (A); Lively's find, Australia (B).
C- Section of the outer rim of a gold granule from
«Black placer», Arizona (A); note the spongy morphology
and the light gray color, indicative of less presence of
copper and silver.
(Figure number 7 from Melchiorre et alii., 2018)[10]

1 2 3 4 5 6
1. Surface conditions Establishment of other bacterial species and biofilm growth 5. Mobilization of gold 6. Cell dispersion
Acinetobacter spp.
Lysobacter sp.
Duganella sp.
Solubilization of gold (S)
Detoxification from gold (G)
Resistance to metal (M)
4. Metabolic turnover of complex
compunds
Complessi organici (O);
Xenobiotici (X);
Tossine (T);
3. Nutritional cicle
C- fixation (C)
N2- fixation (N)
Nitrificazione (NI)
Denitrificazione (D)
2. Production EPS (E)
Auto-aggregation (A)
Diaphorobacter sp. (S)
Sphingomonas spp. (S, M)
Methylobacterium sp. (S)
C. metallidurans (G)
D. adovorans (G)
S. maltophilia (G)
Achromobacter spp. (M)
Halomonas sp. (M)
Herbaspirillum sp. (M)
Burkholderia spp. (M)
Shewanella sp. (M)
Acinetobacter spp. (M)
Pseudomonas spp. (M)
Ideonella sp. (M)
Acinetobacter spp. (O)
Burkholderia spp. (O)
Pelomonas sp. (O)
Pseudomonas spp. (O)
Sphingobium sp. (O)
Sphingomonas spp. (O)
Arthrobacter sp. (X)
Diaphorobacter sp. (X)
Phenylobacterium sp. (X)
Xanthomonas sp. (X)
Methylobacterium sp. (T)
Rhodobacter sp. (C)
Beijerinckia sp. (N)
Rhizobium spp. (N)
Herbasiprillum sp. (N)
Pelomonas sp. (N)
Nitrobacter sp. (NI)
Diaphorobacter sp. (NI, D)
Acidovorax sp. (D)
Achromobacter sp. (D)
C. Metallidurans (D)
S. Maltophilia (D)
Pseudomonas spp. (D)
Pseudomonas spp. (E)
Burkholderia spp. (E)
Methylobacterium sp. (E)
Acinetobacter spp. (E)
Sediminibacterium spp. (A)
Rhodobacter sp. (A)
Arthrobacter spp.
Corybacterium sp.
Deinococcus sp.
Kocuria sp.
Microbacterium spp.
Micrococcus spp.
Propionibacterium spp.
Staphylococcus spp.
Biogenic gold
Secondary gold
Gram – positive bacteria
Gram – negative bacteria
Organic compound
Nano-particled gold
Gold complexes
(modificied from figurr number 6 from Rea et alii., 2016)[9]

9
10- secondary gold dispersed in superficial gold deposits:
A: appearance of secondary gold in granules and macroscopic specks;
B: single gold element in nugget (nugget), Australia;
C: single gold element in grain (picker) (Arrowtown, New Zealand); notice
the superficial traces of iron and manganese oxides, typical indicators of past bacterial activity.
(Figure number 1 from Melchiorre et alii., 2018)[10]

Concentration
Dispersion
Re-concentration
Primary auriferous mineralization (DAP) (Au: 60-90 wt%)
Secondary and bacteria mediated gold (Au: 99 wt%)
Bio-solubilization
Trasportation
Bio-accumulation
Bio-mineralization
Bio-mineralization
Geochemical
process
Silica sinter formation
Sulfides mineralization
Reductive mineralization
Sulfides alteration
Bio-oxidation e
complexation
Radical apparatuses
vegetation
Abiotic mechanisms
(including: capillarity,
convection, diffusion)
Reductive
precipitation
Passive absorption
Nucleation and
crystallization
Fossilization
Uplift
Diagenesis
Metamorphism
Sedimentation
Genesis energy
Genesis energy
Thermophilic and hyperthermophilic
bacteria and Archea
Thermophilic and hyperthermophilic
bacteria SRB (Thermodesulfobacterium spp.)
And Archea (Archaeoglobus spp.) (T <400 °
C)
Hyperthermophile H2 oxidizing bacteria (T.
maritime) and Archea (P. islandicum, P.
furious) (T <400C)
Fe / S oxidation
Cyanide production
Production of
amino acids
Thiosulfate
production
Vegetation - bacteria interaction:
Essutation of roots, metabolism
Detossification
Micronutrition
Genesis energy
Use of the ligand
R. metallidurans, S. enterica, P. boryanum
M. luteus, methanotrophic bacteria (?)
G. metallireduces, R. metallidurans (?)
Fe / S oxidising (gold thiosulphate) (A. thiooxidans), SRB, amino acid
complexes and cyanurates of gold
Bacteria: P. maltophilia, B. subtilis, E. coli
Yeasts: C. utilis, S. cervisiae
Attinomicets: S. albus, S. fradiae
Fungi: A. niger, F. oxysporum
Fungi, yeasts and bacteria (Pseudomonas spp.)
C. violaceum, P. fluorescens, P. aeruginosa, P. putida, P. syringae,
P. pecoglossicida, B. megaterium
Fungi: (A. niger, F. oxysporum) and bacteria (B. subtills, B. alvei, S.
marcescens, B. megaterium)
Fe/S oxidising (A. thioparus), actinomycetes (S. fradiae), SRB (D.
desulfuricans)
Fe/S oxidising (A. ferrooxidans, A. thiooxidans)
Metamorphic event
Supergenic event
Idrothermal event
Example: quartz pebble conglomerates in gold placers
(Witwatersrand, Africa)
(modified by figure number 1 da Reith et et alii., 2017)

11
1- Theoretical concepts: biogenic cycle of gold
1c- Comparative biotic and abiotic model: from primary mineralization[12] to the finding of gold in surface environments in
the form of secondary gold[13] .
@L’OR Deluy N17 @L’OR Deluy N17[12] [13]
12- Primary gold mineralization (from DAP)
of low temperature (T up to 300°C).
Bacterial activity could result
important in the concentration of gold (T up to 400°C).
13- Secondary gold in which they contribute
both the biotic and the abiotic model.

12
Biogenic gold cycle - Potential in exploration and mining AMI conferenze - Oberto Matteo - October 2018
Biotic model (LE)
Abiotic model
(LE)
Abiotic model
(HE)
Model in which bacterial colonies (biofilms) are
determinants for the biogenic cycle of gold.
Model in which the vegetation, through the capillarity, the exudation
of the root system, etc. allows a localized enrichment of gold.
Model in which the exogenous agents allow a localized
enrichment in gold. Moreover, in the transient moments
between high-energy events, the external rims passively enrich
themselves in gold (Ag-Cu leaching).
Metallogenic
event
Biotic model (LE)
Hydrothermal, metamorphic, etc. event that
generates the primary gold deposit (DAP).
Hyperthermophilic bacterial colonies resistant to
hostile and deep environments allow a localized
enrichment in gold (deep biosphere).
Supergenic
enrichment
Gold granules are not only enriched in
superficial deposits (DAS) but also larger in size
than the primary source (DAP).
Primary gold
deposit
(DAP)
Secondary
gold
(DAS)
Biotic model vs abiotic model[9,10]

13
14- Gold granules and flakes influenced by the high-energy abiotic process (kinetic stress).
1
2
2b
3
4
4b
5
Legend
1- Gold with morphology similar to primary gold mineralization (DAP, DASe);
2, 2b- Gold similar to (1) but with a lower correspondence, higher activity exogenous agents (DASe-c, DASf);
3- Gold flattened in flakes in high-energy environments (rivers, shores) (DASf, DASco);
4, 4b- Gold folded as a result of buckling in high-energy environments (DASf);
5- Gold of greater dimensions following supergenic processes (abiotic).
Abiotic model (high energy environment)[14]
[14]

14
15- schemes that report the main results of the biotic and abiotic model on granules and golden flakes (in section).
Gold grain in which biofilms tend
to pass the present gold in solution
and disperse it in the form of complexes
in the surrounding fluids.
Gold grain in which the rims more
external in contact with the surrounding
environment react, dispersing
silver and passively enriching in gold.
Gold grain in which the process is active
described alongside and locally in the
depressions, biofilms act by fixing the gold
present in the surrounding fluid complexes.
Depressions are over time filled.
a b c
Biotic process
Gold, silver and copper are
dispersed due to biological
activities.
Abiotic process
Silver and copper are
dispersed without biological
activities.
Abiotic e biotic process
Silver and copper are
dispersed without the
biological activities. Biogenic
gold present.
Biotic model (low energy environment)
[15]

16- section of a gold granule in which it is possible to observe in synthesis the chemical differences of the gold-silver-copper alloy and the
compositional ratio between the outer rim, the intermediate portion and the core.
15
15
Minerals included within the
golden grain
Inner core of the
golden grain
External levels of the
golden grain
Intermediate levels of
golden grain
97% Au; 2%Ag;
1% Cu
72% Au; 27%Ag;
1% Cu
68% Au; 30%Ag;
2% Cu
Different
composition
Model contribution:
M. Low-energy biotic;
M. Low-energy abiotic;
M. High-energy abiotic.
Contribution of the main processes related to the
metallogenic event.
Possible depression in which
bacterial colonies can nest.
[16]
< Ag; > Au

16
17- in the following image are summarized the gold granules resulting from predominantly biotic processes (left) and abiotic processes (right).
Abiotic model[9,17]:
Model in which the granules and golden flakes increase in size
thanks to the weak forces of attraction in high energy environments,
which allow a higher percentage of gold particles in contact over time.
Biotic model[9,17]:
Model in which the granules and golden flakes increase
in size thanks to the precipitation of biogenic gold
in the main depressions. One is generated protective
film that covers the original granule.
Pro:
- Favorable coastal and river environments;
- Explain the nuggets found in coastal and river placers;
Versus:
- Difficult calculation of probabilities;
- The morphology does not show a clear correspondence;
Pro:
- Favorable tropical, subtropical and temperate environments;
- Explain the nuggets found in lateritic soils;
- Explain the silver and platinum nuggets;
Versus:
- Difficult interdisciplinary studies;
- Bacteria tend not to leave a trace of their past presence on
the affected gold granules;
[17]

17
Note how the main DAS are flanked by those produced by exogenous agents with less influence.
Rushing waters
DASc
Wind action
DASeo
Genesis of soils
DASlat
Glacier
DASg
Dominant
exogenous agent
generates
main DAS
Less influential exogenous agent reworks the main DAS
DASe-c
DASfr
DASfr-c
DASg
DASf
DASf-c
Canale attivo
Hydrothermal gold-mineralized system
DASe
[18]
Theoretical concepts: biogenic cycle of gold:
1d- Influence of the biotic and abiotic model
18- longitudinal profile to the slope in which are reported the various secondary gold deposits (DAS), generated by the prevailing local
exogenous agents. The gold present, its size and its concentration depend on the relationship between the abiotic and biotic processes and
how they vary in time and space.

18
Theoretical concepts: biogenic cycle of gold:
1e- The role of vegetation associated with the
biogenic cycle of gold[9,10,19,20] ;
19- soil profile in which it is possible to highlight localized enrichment portions in biogenic gold (yellow dotted).
[19]

19
20- longitudinal profile to the slope where it is shown how the dispersion of the characteristic elements of the primary mineralization
(pathfinder) and of the gold itself are also influenced by the biosphere, as well as by the hydrosphere (flow direction of the groundwater).
Portions in which the chemical and bacterial leaching are dominant.
Portions in which the bioaccumulation and the bio-precipitation are dominant.
[20]

20
2- Potential in mining exploration
2a- Geochemistry of heavy sediments[21,22]
In the first prospecting phases it is possible to carry out a study on the heavy terrigenous fraction, which can
be sampled along the main watercourses. It highlights the possible primary gold-mineralizations. The gold
contained in the sulphides is found typically free, as these are easily alterable and release the noble metal.
[21] [22]
21 - sieving in the column: a series of sieves with finer meshes downwards allow to provide quantitative information on the dimensions of
the main minerals sought. There is also a first qualitative approach on the ground.
22- following a geochemical exploration of heavy sediments it is possible to determine and locate the content calculated by the samples
and to have indications on primary mineralization.

21
2b- Geochemistry of soils and land adjacent to the DAP[23,24]
The application of a soil sampling campaign at different depths using standard methods can lead to the
spatial placement of the researched deposit and its characterization (constituent minerals, probable content,
size of the deposit, etc.). Usually this prospecting phase is preceded by the geochemical phase of heavy
sediments[21,22] ;
[23] [24]
23- longitudinal section to the slope in which the chemical anomaly of the gold at the sample closest to the buried mineralization is
highlighted. The term "wall rock" refers to the ore host rock.
24- samples are taken according to standard instructions and at known depths, according to the type of geochemical campaign requested.

22
biogeochemistry
Geochemistry outcrops
Geochemistry of heavy
sediments
Geochemistry of lake
sediments
Geochemistry of soil gases
Primary auriferous
mineralization
(DAP)
Secondary
dispersion
Primary
dispersion
Geochemical waters
underground
Embedding geochemistry
of mineralization
Plume of dispersion of the
pathfinder elements typical of
mineralization
Geochemistry of soil and
regolite
Lateritic soil
Non lateritic soil
Regolite
[modified 25]
25- a three-dimensional model that highlights the spatial relationships between primary and secondary dispersion plumes with respect to
a buried auriferous deposit (DAP). There are various approaches to geochemical analysis applicable.

23
2- Potential in mining exploration:
2c- Biosensing and recognition of bacterial association (e.g. C. metallidurans)[9,10,11,26,27];
Biosensors are devices that use microorganisms to detect specific compounds; the binding of the sensor, which is
usually an enzyme, results in a measurable change. These specific proteins could theoretically be used to immediately
detect and quantify gold concentrations in environmental samples. You can detect gold concentration values up to 20
ppb with accuracy of 2 ppb. This technique can also be used on the ground.
[26] [27]
26- Ultra-thin section in which Cupriavidus metallidurans is observed with particulate gold in the cytoplasm.
27- biofilm in which C. metallidurans is present in the depression of a gold granule.

24
3- Potential in the mining sector
3a- Bioprocessing (bioleaching)[9,10,11] ;
Gold is extracted from calaverite (AuTe2)[28] , silvanite (Ag, Au)Te2, petzite (Ag3AuTe2) as well as
sulfides[29]:
• Biolisciviation of pyrite with Thiobacillus ferrooxidans;
• Biolisciviation of gold with Diaphorobacter sp.
• Bioaccumulation of gold with C. metallidurans;
[28] [29]
28- calaverite in quartz matrix, size of the mineral in photograph about a centimeter.
29- biofilm in which T. ferrooxidans is present, which oxidizes arsenopyrite and releases gold over time.

25
4- Conclusions
The influence of microorganisms (archea, bacteria, fungi, yeasts) on the increase in the size of the gold
granules and nuggets in superficial (e.g. placer) and deep environments (e.g. deposits) it could be greater
than previously hypothesized[30] . The biotic and abiotic models combine together to increase both the size
and to enrich physical portions in gold[31] . On the basis of many factors (e.g. the climate) it is possible that
the models prevail over time of importance one on the other[9,10,11] .
[30] [31]
30- nuggets of different sizes and origins (United States, Canada); notice the different morphology, can we distinguish biogenic gold?
31- private collection: nuggets, granules and speckles of different sizes, the action of exogenous agents is important; provenance: Canada
@L’OR Deluy N17 @L’OR Deluy N17

26
Thanks for the attention
I spent the whole
weekend
proliferating
Bacteria life
but good, you had
fun !?
yes but
now I do
not know
where to
put them!

27
For further information on the topics covered made by the author
In press In production

28
For further information on the topics covered
Available Available

29
5- Bibliography and sitography
1. Photo courtesy of the author of the Facebook page: L'OR Dely N17 - Official Gazette No. 17.
https://www.facebook.com/Deluyd/photos/a.945455728853375.1073741829.667599346639016/1631353413596933/?type=3&theat
er
2. Photo of Giorgio Bogni's repertoire, "Minerals and Pietre" shop in Sesto Calende, Piazza Mazzini. Photography shoots in March 2018,
find in 2017 at external supplier.
3. Photo courtesy of the Facebook page: L'OR Deluy N17 - Official Gazette No. 17.
https://www.facebook.com/Deluyd/photos/a.945455728853375.1073741829.667599346639016/1631328336932774/?type=3&theat
er
4. The characteristics of the bacterial cell: http://www.chimica-online.it/biologia/batteri.htm
5. http://www.treccani.it/enciclopedia/batteri/
6. https://www.ck12.org/biology/bacteria-reproduction/lesson/Prokaryote-Reproduction-BIO/
7. http://english.mathrubhumi.com/news/columns/faunaforum/bacteria-are-everywhere%21-english-news-1.1270282
8. Further external coverings: http://www.chimica-online.it/biologia/batteri.htm
9. Rea Maria Angelica, Zammit Carla M. & Reith Frank - Bacterial biofilms on gold grains - Implication for geomicrobial transformations of
gold. (2016). FEMS Microbiology Ecology, 92, 2016, fiw082.
10. Melchiorre Erick B., Orwin Paul M., Reith F., Rea D. Maria Angelica, Yahn J & Allison R. - Biological and geochemical dvelpment of
placer gold deposits at Rich Hill, Arizona USA (2018). Minerals 2018, 8, 56; doi: 10-3390 / min8020056; www.mdpi.com/journal /
minerals.
11. Reith F., Lengke M., Falconer D., Craw D., Southam G. - The geomicrobiology of gold (2007). The ISME Journal (2007) 1, 567-584 @
2007 International Society fro Microbial Ecology. All rights reserved 1751-7362 / 08. www.nature.com/ismej
12. Photo of repertoire kindly provided by the Facebook page: L'OR Deluy N17 - Official Gazette No. 17.
14. Author's repertory image;
21. https://steemit.com/africa/@sayodele52/gold-exploration-using-stream-sediments
22. https://www.geologyforinvestors.com/geological-field-work-when-is-it-justified/
23. http://www.medellin.unal.edu.co/~rrodriguez/geologia/anatomy-of-a-mine/Anatomy%20of%20a%20Mine%20--%20Exploration%20-
%20Continued1.htm
24. https://www.ngu.no/en/topic/geochemical-prospecting
25. https://www.slideshare.net/DEEPCHANDBALAMANI/geochemical-drainage-surveys
26. https://www.internetchemie.info/news/2009/oct09/images/cupriavidus-metallidurans.jpg
27. https://en.wikipedia.org/wiki/Cupriavidus_metallidurans#/media/File:CSIRO_ScienceImage_3908_Coloured_scanning_electron_imag
e_of_bacterioform_gold_on_a_gold_grain_from_the_Hit_or_Miss_Mine_in_northern_Queensland.jpg
28. https://e-rocks.com/item/cr193577/calaverite
29. https://www.hzdr.de/db/Cms?pNid=610

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