Hydrothermal Process 3p6s20

HYDROTHERMAL PROCESS-THE TERM HYDROTHERMAL MEANS HOT WATER, AND HOT WATERS MAY ORIGINATE BY OTHER THAN MAGMATIC PROCESSES •

LINDGREN HAS DESIGNATED THESE THREE GROUPS AS: -HYPOTHERMAL -MESOTHERMAL -EPITHERMAL

HYPOTHERMAL-IN FAVORABLE HOST ROCKS, REPLACEMENT DOMINATES UNDER THE CONDITIONS OF HIGH TEMOERATURES AND PREASSURES NEARER THE INTRUSIVE WHERE HYPOTHERMAL DEPOSITS ARE FORMED EPITHERMAL- CAVITY FILLING DOMINATES UNDER THE CONDITIONS OF LOW TEMPERATURES AND PRESSURES WHERE EPITHERMAL DEPOSITS ARE FORMED. MESOTHERMAL-BOTH THE HYPOTHERMAL AND EPITHERMAL ARE THE CHARACTERISTICS OF THE MESOTHERMAL ZONE. TELETHERMAL DEPOSITS-DEPOSITS FORMED BY SOLUTIONS THAT MIGRATE FAR FROM THE INTRUSIVE, OR POSSIBLY ARE NOT DERIVED FROM THE INTRUSION AT ALL, MAY APPROACH THE TEMPERATURE OF THE HOST ROCK.THEY GENERALLY PRODUCED ONLY WEAK REACTIONS AND ARE REFERRED TO AS TELETHERMAL DEPOSITS XENOTHERMAL DEPOSITS- MAY EXHIBIT HYPOTHERMAL TO EPITHERMAL MINERALOGY BUT IN OVERLAPPING OR TELESCOPIC CONFIGURATION. HYDROTHERMAL PROCESSES-IN THEIR JOURNEY THROUGH THE ROCKS, THE HYDROTHERMAL SOLUTIONS MAY LOSE THEIR MINERAL CONTENT BY DEPOSITION IN THE VARIOUS KINDS OF OPENINGS IN THE ROCKS, TO FORM CAVITY FILLING DEPOSITS, OR BY METASOMATIC REPLACEMENT OF THE ROCKS TO FORM REPLACEMENT DEPOSITS. Hydrothermal Deposits-Hydrothermal mineral deposits are those in which hot, mineral laden water (hydrothermal solution) serves as a concentrating, transporting, and depositing agent. Conditions necessary for the formation of hydrothermal ore deposits include: a)

Presence of hot water to dissolve and transport minerals

b) Presence of interconnected openings in the rock to allow the solutions to move c)

Availability of sites for the deposits, and

d)

Chemical reaction that will result in deposition

Hydrothermal mineral deposit,-any concentration of metallic minerals formed by the precipitation of solids from hot mineral-laden water (hydrothermal solution).

Hydrothermal Deposits Forming Today Imperial Valley, southern California -In 1962, oil/gas drilling struck a 350°C brine at 1.5 km depth. As the brine flowed upwards and cooled, it deposited a siliceous scale. Red Sea -In 1964, oceanographers discovered a sries of hot, dense brines at the bottom of the Red Sea. The higher density of the brines (i.e. increased sanility) means that they remain at the bottom of the sea, despite being hot. East Pacific Rise -In 1978, deep-sea submarines on the East Pacific Rise, at 21°N, found 300°C hot springs emerging in plumes along the oceanic ridge, 2500 m below sea level. Skarns Deposits-Skarns are generally thought of as being the result of metamorphism of impure limestone. Exoskarns are skarns developed in the sedimentary rocks surrounding the themal source (pluton). Endoskarns are those developed within the igneous intrusion. For hydrothermal deposits to form a number of criteria needed to be satisfied like :  Highly active fluids containing ions such as O2_,F_,OH_ etc. to form complexes with metal ions and dissove metals in it  Suitable pathways( cracks,fissures,pores and other open spaces) for the fluid solutions to through surrounding rocks  Physico-chemical factors responsible for deposition ESSENTIALS FOR THE FORMATION OF HYDROTHERMAL DEPOSITS ARE: 1. AVAILABLE MINERALIZING SOLUTIONS CAPABLE OF DISSOLVING AND TRANSPORTING MINERAL MATTER 2. AVAILABLE OPENINGS IN ROCKS THROUGH WHICH THE SOLUTIONS MAY BE CHANNELED 3.AVAILABLE SITES FOR THE DEPOSITION OF MINERAL CONTENT 4. CHEMICAL REACTIONS THAT RESULT IN DEPOSITION 5. SUFFICIENT CONCENTRATIONS OF DEPOSITED MINERAL MATTER TO CONSTITUTE WORKABLE DEPOSITS. CAVITY FILLING-THE FILLING OF OPENINGS OR CAVITIES IN THE ROCKS WAS EARLY THOUGHT TO BE THE ONLY MODE OF FORMATION OF MINERAL DEPOSITS AND FOR LONG WAS CONSIDERED THE MOST IMPORTANT. SUCCESIVE CRUSTS OFUNLIKE MINERALS DEPOSITED UPON THE WALLS OF OPEN SPACES GIVE RISE TO CRUSTIFICATION AND WHERE SUCH CRUSTS SURROUND BRECCIA FRAGMENTS, COCKADE ORE MAY RESULT.

THE CRUSTIFICATION MAY BE SYMMETRICAL WITH SIMILAR CRUSTS ON EITHER SIDE OR ASYMMETRICAL, WITH UNLIKE BANDS ON EITHER SIDE. CRUSTIFICATION IS QUITE DIAGNOTIC OF CAVITY FILLING. IF THE FILLING CONSISTS OF ONLY ONE MINERAL SUCH AS QUARTZ, COMB STRUCTURE OR CRUSTIFICATION MAY NOT BE PRESENT AND THE FILLING IS SAID TO BE MASSIVE. ORIGINAL CAVITIES 1. PORE SPACES- ROCK PORES ARE INTRSTITIAL OPENINGS BETWEEN GRAINS, CAPABLE OF ABSORBING FLUIDS. - THEY MAKE ROCKS PERMEABLE AND SERVE AS CONTAINERS FOR ORES, PETROLEUM, GAS AND WATER. 2. VESICLES OR “BLOW HOLES” -ARE OPENINGS PRODUCED BY EXPANDING VAPORS TYPICAL OF THE UPPER PART OF MANY BASALTIC LAVA FLOWS. 3. BRECCIA AGGLOMERATE SPACES - VOLCANIC BRECCIAS (AGGLOMERATES) COMPRISE BLOCKS OF LAVA IN AN ASH MATRIX AND ARE THE PRODUCT OF AN EXPLOSIVE ERUPTION. -HYDROTHERMAL BRECCIAS ARE FORMED WHEN HYDROTHERMAL FLUID FRACTURES A ROCK MASS. 4. COOLING CRACKS - FORMED AT HIGH TEMPERATURES WHEN A BASIC MAGMA IS EITHER VISCOUS OR CRYSTALLINE AND HOT.

INDUCED OR SUBSEQUENT CAVITIES 1. FISSURES, WITH OR WITHOUT FAULTING- CONTINOUS TABULAR OPENINGS IN ROCKS, GENERALLY OF CONSIDERABLE LENGTH AND DEPTH. 2. SHEARING CAVITIES- SHEAR ZONE RESULTS EHERE FRACTURES, INSTEAD OF BEING CONCENTRATED IN ONE OR TWO SINGLE BREAKS, ARE EXPRESSED IN INNUMERABLE CLOSELY SPACED AND MORE OR LESS PARALLEL, DISCONTINOUS SURFACES OF DEEP-SEATED RUPTURE AND CRUSHING.

3. CAVITIES DUE TO FOLDING AND WARPING- FLEXING AND FOLDING OF SEDIMENTARY STRATA GIVES RISE TO : 1. SADDLE REEF OPENINGS 2. PITCHES 3. LONGITUDINAL CRACKS

4. SOLUTION CAVES- A CAVITY FORMED IN CERTAIN ROCKS IN WHICH PERCOLATING SOLLUTIONS HAVE FILLED WITH VALUABLE MINERALS. 5. TECTONIC BRECCIAS- IT IS A FAULT BRECCIA FORMED BY TECTONIC FORCES, AND A ROCK TYPE CONSISTING OF ANGULAR CLASTS. 6. IGNEOUS BRECCIAS- IGNEOUS BRECCIAS ARE OF TWO TYPES: VOLCANIC BRECCIA FORMING AGGLOMERATES, AND INTRUSIVE BRECCIAS. BOTH CONSISTS OF COARSELY AND ANGULARLY FRAGMENTED IGNEOUS ROCKS WITH FINER INTERSTITIAL MATERIAL. 7. VOLCANIC PIPES- WHEN EXPLOSIVE VOLCANIC ACTIVITY BORES PIPELIKE OPENINGS, THE MATERIAL BLOWN OUT MAY FALL BACK OR BE ASTED BACK INTO THE OPENING, FORMING AN ANGULAR BRECCIA WITH SPACES BETWEEN FRAGMENTS. 8. ROCK ALTERATION OPENINGS WALL ROCKS THAT HAVE BEEN ALTERED BY SOLUTIONS ARE FOUND BY TESTS TO BE GENERALLY MORE POROUS THAN UNALTERED ROCKS AND PERMIT THE INGRESS OF MINERALIZING SOLUTIONS

DEPOSITS RESULTING FROM CAVITY FILLING •

FISSURE VEINS-A FISSURE VEIN IS A TABULAR ORE BODY THAT OCCUPIES ONE OR MORE FISSURES; TWO OF IT’S DIMENSIONS ARE MUCH GREATER THAN THE THIRD. FISSURE VEINS ARE THE MOST WIDESPREAD AND MOST IMPORTANT CAVITY FILLINGS AND YIELD A GREAT VARIETY OF MINERALS AND METALS.

VARIETIES: THE VARIETIES OF FISSURE VEINS ARE: 1. SIMPLE 2. COMPOSITE 3. LINKED 4. SHEETED 5. DILATED 6. CHAMBERED

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SHEAR ZONE DEPOSITS-MOST FISSURES VEINS ARE NARROW AND RANGE IN LENGTH FROM A FEW TENS OF FEET TO A FEW MILES.

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STOCKWORKS--A STOCKWORK IS A MASS OF ROCK TRAVERSED BY AN INTERLACING NETWORK OF SMALL RE-BEARING VEINLETS. THE INDIVIDUAL VEINLETS RARELY EXCEED AN INCH OR SO IN WIDTH, A FEW FEET IN LENGTH, AND THEY ARE SPACED A FEW INCHES TO A FEW FEET APART.

STOCKWORK VEINLETS ARE FORMED BY: 1. CONTRACTION UPON COOLING OF THE UPPER AND MARGINAL PARTS OF INTRUSIVE IGNEOUS ROCKS. 2. IRREGULAR FISSURES PRODUCED BY TENSIONAL OR TORSIONAL FORCES.

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SADDLE WORKS- IF A THICK STACK OF WRITING PAPER IS SHARPLY AREHED, OPENINGS FORM BETWEEN THE SHEETS AT THE CREST OF THE ARCH.

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LADDER VEINS-”LADDER VEINS” IS THE NAME APPLIED TO MORE OR LESS REGULARLY SPACED, SHORT, TRANSVERSE FRACTURES IN DIKES.

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TENSION CRACK FILLINGS, PITCHES AND FLATS-UNDER LIGHT LOAD, SLUMPING OR GENTLE SYNCLINICAL FOLDING OF BRITTLE SEDIMENTARY BEDS GIVES RISE TO A SERIES OF CONCERNED TENSION CRACKS OR OPENINGS COLLECTIVELY KNOWN AS PITCHES AND FLATS.

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SOLUTION CAVITY FILLINGS-VARIOUS TYPES OF SOLUTION OPENINGS IN SOLUBLE ROCKS HAVE AFFORDED RECEPTACLES FOR PRIMARY AND SECONDARY MINERALS DEPOSITS

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BRECCIA FILLING DEPOSITS- THE HAPHAZARD ARRANGEMENT OF THE ANGULAR ROCK FRAGMENTS IN BRECCIAS GIVES RISE TO NUMEROUS OPENINGS THAT PERMIT THE ENTRY OF SOLUTIONS AND MINERAL DEPOSITION, FORMING BRECCIA FILLING DEPOSIT.

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VOLCANIC BRECCIA DEPOSITS-EXPLOSIVE VOLCANIC ACTIVITY GIVES RISE TO BEDDED BRECCIA DEPOSITS AND BRECCIA PIPES OR CRATERS.

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COLLAPSE BRECCIA DEPOSITS-IN THE CAVING METHODS OF MINING, AN EXCAVATION IS STARTED BELOW; THE ROOF ROCK THEN CAVES AND GRADUALLY EXTENDS ITSELF UPWARD UNTIL THE WHOLE CAVED BLOCK IS A MASS OF JUMBLED, ANGULAR FRAGMENTS OF ORE WITH CONSIDERABLE PORE SPACE.

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TECTONIC BRECCIA DEPOSITS-BRCCIAS PRODUCED BY FOLDING, FAULTING, INTRUSION, OR OTHER TECTONIC FORCES HAVE BEEN REFERRED TO VARIOUSLY AS CRUSH, CRACKLE, AND SHATTER BRECCIAS.

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PORE SPACES FILLINGS-PORE SPACES MAKE ROCKS PERMEABLE AND SERVE AS CONTAINERS FOR ORES, PETRLEUM GAS, AND WATER.

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VESICULAR FILLINGS - VESICULAR LAVAS, PRODUCED BY EXPANDING VAPORS, ARE TYPICAL OF THE UPPER PART OF MANY BASALTIC FLOWS.

FACTORS THAT DETERMINE THE TYPES AND INTENSITIES OF HYDROTHERMAL ALTERATIONS ARE: •

CHARACTERISTICS AND COMPOSITION OF THE HOST ROCK

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COMPOSITION OF THE HYDROTHERMAL FLUID

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TEMPERATURE AND PRESSURE CONDITIONS AND CHANGES IN PHASE OF THE HYDROTHERMAL FLUID

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CHANGES IN CERTAIN CONSTITUENTS SUCH AS EARLY RELEASED H2S THAT MAY BECOME A STRONG ACID

HYDROTHERMAL ALTERATION-THE RECOGNITION AND APPLICATION OF THE VARIOUS TYPES OF HYDROTHERMAL ALTERATION OR WALL ROCK ALTRATION HAS PROVIDED A VALUABLE PRIME EXPLORATION TOOL THAT MUST BE USED BY THE EXPLORATION GEOLOGIST BECAUSE THE ALTERATION HALO IS MUCH MORE WIDESPREAD THAN THE SMALLER TARGET OF A HIDDEN ORE DEPOSIT. TYPES OF HYDROTHERMAL ALTERATIONS •

DOLOMIZATION-VARIABLE AMOUNTS OF MAGNESIUM SUBSTITUTING FOR CALCIUM IN CARBONATE ROCKS COMMONLY OCCURS IN SEDIMENTARY PROCESSES.

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SILICIFICATION- THE ADDITION OF QUARTZ OR OPALINE SILICA TO THE OTHER ROCKS IN DEPOSITS IS WELL DISPLAYED.

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ARGILLIC ALTERATION- THIS TERM WAS SUGGESTD BY LOVERING IN 1940 TO EMPHASIZE THE PREVELANCE OF CLAY MINERALS FORMED BY HYPOGENE SOLUTIONS REACTING WITH WALL ROCKS CONCORDANT WITH THE LEACHING OF LIME.

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SERICITIZATION-SERICITIC OR POTASSIC ALTERATION IS PROBABLY THE MOST ABUNDANT, MORE READILY RECOGNIZED, AND WIDESPREAD VARIETY OF ALTERATION NOTED.

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PROPYLITIC ALTERATION

-THIS TYPE OF HYDROTHERMAL ALTERATION HAS BEEN LESS COMMONLY RECOGNIZED IN THE PAST, ESPECIALLY IN PORPHYRY COPPER DEPOSITS, BUT THE LARGE ASSEMBLAGE OF MINERALS INCLUDED IN THIS TYPE OF ALTERATION MAKES IT RECOGNITION OF SIGNIFICANT IMPORTANCE