Anomaly detection plays an essential role within process mining systems, significantly impacting enhanced operational security measures for IT networks through various mechanisms:

1. **Abnormality Identification**: Anomaly detection algorithms leverage statistical or machine learning methods to identify patterns deemed unusual or unexpected within data streams extracted from IT network activities. This identification helps in recognizing deviations that might signal potential threats.

2. **Threat Prevention**: By detecting anomalies promptly, organizations can implement additional layers of security measures around identified suspicious behaviors before these could cause significant harm. For instance, an anomaly in access authorization processes could indicate unauthorized or malicious activity requiring immediate attention.

3. **Enhancing Response Speed**: In IT network operations management systems like process mining repositories, timely responses are crucial during cyber incidents detection and response stages(anomaly alert). Anomaly detection systems can significantly speed up the identification timelines of threats, allowing for quicker intervention measures to be enacted swiftly.

4. **Continuous Monitoring**: Process mining processes continuously analyze operational data streams looking for deviations from norms in IT network activities which might indicate underlying security risks. This continuous monitoring ensures that threat surfaces are detected promptly irrespective of when they arise within data feeds.

5. **Operational Efficiency Improvement**: Beyond just identifying anomalies, these systems contribute positively towards enhancing efficiency metrics within the IT networks by providing insights into suboptimal behaviors and process inefficiencies requiring attention for better performance outcomes without compromising security protocols.

6. **Compliance Assurance**: Anomaly detection can help ensure regulatory compliance in IT networks activities where certain deviations might indicate potential non-conformity with established guidelines or standards governing network operations management systems.

In essence, the role of anomaly detection within process mining and its impact on operational security for IT networks lies critically in providing a real-time surveillance system capable of identifying threats preemptively amidst vast volumes of data flow common within complex IT infrastructures. Its application thus is instrumental towards fostering secured operations while maintaining high performance levels essential for smooth network functioning.

Please note that this discussion provides high-level insights into anomaly detection's role in process mining systems pertaining operational security measures without detailing specific technical mechanisms utilized therein nor delving into practical examples of implementation across diverse industry sectors for which process mining systems might be deployed.