Administrative Assistant

About Mariana Minerals

Mariana Minerals is a software-first, vertically integrated minerals company on a mission to supply the critical minerals powering modern energy, AI, and defense technologies. We’re reimagining the minerals supply chain by combining deep industry expertise with advanced software, automation, and data-driven decision-making.

The Role

We are seeking a highly organized and proactive Administrative Assistant to support day-to-day administrative operations at our Houston office. This role is ideal for someone early in their career who is detail-oriented, resourceful, and eager to grow within an operations or executive support function.

The Administrative Assistant will provide administrative support to the CFO, including calendar and travel coordination and expense management, while also supporting day-to-day office operations. The role will also serve as backup to the Executive Assistant as needed. This position requires strong communication skills, flexibility, sound judgment, and the ability to manage competing priorities in a fast-paced environment.

What You’ll Do

Administrative & Calendar Support

• Assist with scheduling meetings, managing calendars, and coordinating internal and external appointments

• Help prepare meeting materials, agendas, and notes as needed

• Support coordination of cross-functional meetings and company events

Travel & Logistics

• Book and manage domestic and international travel (flights, hotels, ground transportation)

• Handle last-minute travel changes and troubleshoot logistical issues

Expense & Reporting Support

• Prepare and submit expense reports in a timely and accurate manner

• Reconcile receipts and assist with tracking budgets or spending reports

On-Site & Office Support

• Provide in-office support as needed

• Coordinate office supplies, deliveries, and facilities-related requests

• Assist with visitor management and on-site meeting logistics

• Support internal events and team off-sites

Executive Assistant Backup

• Serve as backup to the Executive Assistant during absences

• Provide overflow support during high-volume periods

• Assist with special projects and ad hoc requests

Desired Qualifications

• 1–3+ years of administrative or office support experience preferred

• Strong organizational skills and attention to detail

• Excellent written and verbal communication skills

• Proficiency in Microsoft Office

• Experience with expense management and calendar systems preferred

• Ability to handle confidential information with discretion

• Strong time management and prioritization skills

• Problem-solving mindset

• Professional and service-oriented approach

• Adaptability in a fast-paced environment

• Team player with a positive attitude

Our culture is built on four principles:

Everyone Gets Home Safe. We never put speed or cost ahead of people.

Extreme Ownership. We take full responsibility for outcomes, relentlessly driving toward solutions.

Engineer Out Requirements, then Automate. We simplify, optimize, and then automate for scale.

Share Your Legos. We collaborate openly, share knowledge, and empower each other to build bigger, better solutions.

Join us as we build the future of responsible mineral sourcing and supply!