JON HRONSKYUNCOVER MINERAL SYSTEMS WORKSHOP

2 JULY 2013

The WMS Approach to Predictive Targeting using the Mineral System Method:

A Dynamic, Fluid-Centric Approach

1

Basic Physics of Ore Formation

2

Diffuse Metal Source Region

Concentrated Metal Deposit

Advective Fluid flux (= Energy Flow)

Fluid Sink

Context:The Evolution of Perspective in

Economic Geology

3

Ore specimen-centric

Host Rock -centric

Structure-centric

Fluid Flux-centric

Early 1900s

21 st Century

Increasing Scale of Observation

A Key New Concept: Ore-formation as a Self-Organized

Critical System

4Fluid (Energy) Source

Fluid Reservoir

Fluid Sink

Transient Exit Conduit

Threshold Barrier(need not be a physical seal)

Thermal halo - produced by entropy dumped into environment

Episodic focused energy and mass flux

Slow persistent fluid flux

5

Electric Charges Accumulate Slowly

Threshold Barrier:Resistive Air

Ground

Transient Rapid Breach of Threshold Barrier

The Lightning Analogy for Ore-Forming Systems

6

Electric Charges Accumulate Slowly

Threshold Barrier:Resistive Air

Ground

Transient Rapid Breach of Threshold Barrier

The Lightning Analogy for Ore-Forming Systems

7

Regional Scale

Camp Scale

Deposit Scale

Mineral System Framework 1:Ore Genesis as the Focus of a Scale-Hierarchical

Fluid-Driven Mass-Concentrative System

Critical Geochemical

Elements can be mapped to this Physics –based

framework

Fertility Proximity toLithosphere-scale

Structure

Favourable(Transient)

Geodynamics

Ore Genesis

Mineral System Framework 2: Ore Genesis as the Conjunction of Three

Independent Sets of Favourable Conditions

8

+ Preservation = Target

Physics of Ore Formation Means Only Certain, Rare Geodynamic Environments

have Ore-Forming Potential

9

ACTIVEFLUID PRODUCTION

NON-DILATIONAL(ie. “TIGHT”)

GEODYNAMIC SETTING

Fluid-flux driven by fluid pressure not tectonic strain – Fluids

organise in this space

ORE FORMATION POTENTIAL

Transient Compression:

Tampakan District, Mindanao

Red area = amount of convergence partitioned into intra-plate shortening

during subduction reversal. From Rohrlach (2002) 10

11

Chiodini et al. (2004)

Extensional Zone: Diffuse Fluid Flow

Compressional Belt: Organised Fluid Flow

12

Application of Mineral Systems Framework 2:Carlin Gold Province Example

13Schematic Section - Continental Crust (Cawood et al, 2013)

Base of Gold Depositional Window-

Porphyry Style deposits

Base of Gold Depositional

Window- Orogenic Gold deposits (more

CO2-rich fluids in retro-arc

positions)

Metallogenic Association

Typical Deposit Types

Emplacement Environment Long TermPreservational Potential

1 Porphyry-suite deposits

Topographical positive Constructional Arcs

Low – typically very high denudation rates (up to 1km per Ma)

2 Rift associated Epithermal, VMS

Topographically negative Rifted Arcs; shallow rifts for Epithermal, deep submarine rifts for VMS

Low for Epithermals in shallow rifts;Moderate for VMS in deeper rifts (syn-

cycle reworking and erosional possible)

3 Orogenic Au Inverted Pericontinental Rift zones right at cratonisation

High – late orogenic timing means limited syn-cycle erosion, particularly in

hot orogens

4 Olympic Dam style IOCGSleeper style Epithermal

Intracontinental rifts or anorogenic sites

High if emplaced post-cratonisationModerate if emplaced during the

orogenic cycle

14

Summary of the Preservational Potential of Major Au(Cu) deposit types that form in Accretionary Orogens

Metallogenic Association framework derived from Hronsky et al (2012); Note that all deposits are susceptible to removal by subsequent unrelated orogenic cycles

15

Example of integrating both Mineral System Frameworks to define a generic targeting model for a particular ore deposit type

(Note -Targeting Elements related to these Constitutive Elements depend on local geological environment;at the province-scale we will also need to consider preservation)

Association 1 (Porphyry Cu Deposits)

Critical Element:High-level component of the Mineral Systems Frameworkl

Constitutive Element:Generic geological manifestation of a critical element for deposit

type of interest

Targeting Element:Specific geological

manifestation of a constitutive element in the area of interest

Mappable Element:Feature that can be directly

observed in available data and which is a proxy for a targeting element (eg magnetic anomaly)

Modified from McCuaig et al (2010)

Framework for Translating a Conceptual Targeting Model into Useful Proxies

Our generic knowledge about a particular ore type

Our local knowledge about a

region

The way we chose to organise our

thinking